I still don’t know if this truck is a 1967 C10 with glass fuses, or a 2004 Silverado with gear driven “Reed Switch” and the BCM is bad or loose ground. G100’s are the core support or engine, G200 is bulk-head or firewall & back of engine, G300 is dash, etc. I can’t tell someone what to do if I don’t know what they are working! If you are not comfortable with a DMM and what you are seeing, like the comment about “Continuity” what is that? No voltage, no current, vehicles and there systems work on both in series circuits and won’t run if not there. Voltage drop is using your DMM, but amperage below 15 amps (With Most Newer DMM’s) require an amp clamp. I have 5 amp clamps and 3 volt meters with one being analog Simpson type. Google “Simpson volt meters). Please help me to help you. As for young, my youngest son just turned 35. He can take things apart, but looses the parts and does not know how to fix it. Just finish a high-end build on my 4L60 trans, rebuilt my AD244 alternator yesterday complete with new slip-ring and updated diode rectifier, bearings and today, TC&G with cam in 03 LS engine. So got stuff happening, but got to sit, so I reply to help someone. Need 4th lumbar fusion & spinal stenosis scraping postponed due to Wuhan Virus. Hospital empty and surgeons home along with 3/4th of nurses, cleaning staff and support as beds are empty and only emergencies are those who got shot over toilet paper. Later!

 

"bad ground" = is basically
1. A high resistance path
2. An intermittent path
3. The connection is a battery when wet.

Why a battery? Dissimilar metals in the presence of an electrolyte creates a battery. That's what creates the corrosion.
An indicator that dissimilar metals will corrode is in the Anodic index. https://en.wikipedia.org/wiki/Galvanic_corrosion

You don't put Aluminum and steel together. Oxides of Aluminum are self-limiting. Oxides of steel (Rust) is not.

A "short" is not a bad ground.

 

Grounding point G201 was corroded.

I was on motorcraft doing some other work and figured I'd poke around a little in the schematics.
My guess after looking:
I'd say the PATS transceiver (e1101011) was down because of the bad g201 causing the transponder key not to be accepted.
But I don't see how the ground could get from the lamps g200 back to the g201 (e1108901) but must be connected inside the overhead console with g200 (e1110201)

 

"bad ground" = is basically
1. A high resistance path
2. An intermittent path
3. The connection is a battery when wet.

Why a battery? Dissimilar metals in the presence of an electrolyte creates a battery. That's what creates the corrosion.
An indicator that dissimilar metals will corrode is in the Anodic index. https://en.wikipedia.org/wiki/Galvanic_corrosion

You don't put Aluminum and steel together. Oxides of Aluminum are self-limiting. Oxides of steel (Rust) is not.

A "short" is not a bad ground.

I agree. A short is not a bad ground. I don't believe I ever suggested it was. Couldn't agree more about galvanic reactions.

 

I'd consider it a bad ground because the module/sensor was badly grounded. Either completely open to ground or too poorly connected to ground. Either way, its ground and bad.

I'm finding that your perspective is the majority view, a bad ground connection is a bad ground. I don't remember everything behind this, it was a long time ago, but from my schooling a bad ground connection is not a bad ground because there are bad grounds that have nothing to do with ground connections. What I do remember related to this is this is the reason why you never directly ground a circuit directly to the battery's negative terminal. In fact having worked mostly in Europe grounding to the battery is illegal\banned and is an immediate vehicle failure during mandatory periodic inspections which all EU countries have.

Interesting thought about the module being badly grounded? I never considered that because I would expect the entire function of the module being effected. The modules have a "module ground" separate from the grounds of the individual circuits through the module. There have been histories of modules getting wet but the effects of this are all over the place if the module works at all.

After eventually finding out an aftermarket keyless entry was added to the vehicle I suspect if the owner had actually followed procedures to solve this problem he would have discovered another, as of yet unmentioned problem that probably still exists. A ground loop or something similar between the keyless remote and somehow to the ignition. Although the dome light ground connection is identified, G201, where the remote's ground connection is has not been identified. I doubt the owner knows. I don't know this for a fact it's just what I suspect.

 

I asked earlier if it was just semantics to differentiate "bad ground" and "bad connection to ground?" Does a bad connection to ground make the ground bad? I don't know and why I asked.

Bad ground - bad connection to ground - they are the same in electronics terms as the depended ground is unreliable for whatever reason.

does the truck start because of a bad ground connection or because of a short to ground through another circuit?

Honestly can't answer that question for sure. I'm from old school automotive, back when you could lift the hood and see the engine. If you wanted to add fog lights you did so by installing them, running a wire from a relay to the lamps and to the battery. The relay control switch was mounted inside either on or under the dash. Today's modern electronics in cars is something I don't have experience with. Aside from my neighbor's car with the chipped key.

To answer this question: "•••ground to another circuit•••" I would have to guess - I said "Guess" that a starter solenoid might be able to pull in from the current a lamp might draw. Probably not the issue in your friend's case - but I suppose there's a chance the light bulb might have low enough resistance that the starter could find a new pathway to ground through the lamp. BUT - interior lights typically are hot powered. When they are grounded THAT is when they light.

I really don't know the answer to your question. All I can imagine is that the computer is being fooled by the dome light. I'm confident G201 has nothing to do with grounding of the starter since they are grounded by their body being bolted to the engine block.

@shortbus I had an S10. 2002. Fuel pump started drawing heavy current. Blew the main computer fuse. Everything shut down and I coasted to the side of the road. Changed the pump and all was well. As for the tail lights - I, too, had to discover that goofy ground block (plastic I think) at the back bumper. The left side tail lights had failed. Frame rail ground went bad for the very reasons you cited. Salt and winter driving. Otherwise that was a great little truck. But I drive a Taco now. (Tacoma for those unfamiliar with the reference to tacos)

 

This whole thread is based on a problem that has come about over the years, Modules controling many things or even most things. When a single circuit is resposable for something working or not, it's fairly easy to find the problem. But when one computerized module controls many things it gets harder and harder to find the real problem. Many of the things in a module share a ground rail, so when a ground is found one place it MAY allow something else to function.

That above is why I never work on Ford products now, and I grew up hating GM and loving Fords. Ford has a module now for everything and many are far away from what they control. Think about a while back with #12 and his Ford Exploder, his problem was finally solved but wasn't what he expected. My oldest son had an Exploder and while he lives far from me we tried to diagnose his problem. And in the end he had to get rid of it, talked him into getting a Chevy and he can't believe how much easier things are to maintain and work on compared to Fords.

 

Ford Exploder

Neighbor had one. For those who don't understand the reference - they like to blow head gaskets. I'm sure it had to do with a specific engine.

Always been a Chevy guy myself. Until I met and married my wife - who was driving an 89 Celica. She loved it. I was amazed at how reliable it was. But in the end I started spending more time under the hood than sitting in the seat. I wanted her out of it but she wasn't letting it go. Not until she wrecked it. From there she went into a Hyundai Sonata. It was a pretty good car. But the sun roof developed a problem with the limit switches. If you opened it too far you had to manually activate the relay in order to close the roof. That was a bother but not a deal breaker. It wasn't until the automatic transmission tried to go into two gears at once. It was then we decided to sell it. She now drives a Venza. She loves how stable it is in the snow. But her driving style, she gets about 17 MPG, whereas I can get almost 22 MPG. My Taco is averaging 18 MPG but that's with winter gas. Summer gas I can average around 23 MPG. More with highway driving. This is my second Taco. Traded in the first because it was four cylinder and I wanted more power. Sacrificed about a mile per gallon but I like the power. Would LOVE a V8, but the Tundra is just too heavy. It also gets around 18 MPG average over all. Plus, it has a poor safety rating.

 

Bad ground - bad connection to ground - they are the same in electronics terms as the depended ground is unreliable for whatever reason.

Probably not the issue in your friend's case -

Yes, the consensus has been bad ground and bad ground connection are one and the same. It's not what I learned but what I learned is irrelevant if most people don't see it the same way. I need to change.

The truck owner isn't a friend. I don't know who the owner is. This all came from a Ford forum where the problem was pegged as a bad ground with no further explanation. Pursuing further explanation led to "I've been doing this for 40 years and I know," which tells me nothing. That's what brought me here. I also was never trying to fix the problem. I wouldn't have needed help with that. I could have followed the procedures outlined in the manuals which the 40 years of experience never suggested or I could have followed the Power Probe procedures. Regardless of being able to fix problem like this, it doesn't mean I would understand what the problem was or what was actually getting fixed. With vehicles this isn't unusual. For example, I gave up a long time ago trying to explain suspensions over problems like why a steering problem is caused by a poor set-up in the rear suspension. Just as some have said, "I wish I had a dollar for every time I heard short," I wish I had a dollar for everyone I've tried to help that thought what separates them and their car from a professional Rally driver is the parts they put on their car. Not even close to being true and all they've done is make a dangerous car. This is something I do understand.

I appreciate everyone's input to this and don't mean to shut it down to further input but I think I've gotten the answers I came for.

 

The challenge in most motor vehicles comes mostly from using body metal as part of the power and control circuit. Of course it cuts costs and it also reduces weight a small amount. But the weight of 100 feet of ground wire is totally offset by the weight of one power-seat adjusting mechanism. So it all gets down to priorities and cost reductions.

 

The challenge in most motor vehicles comes mostly from using body metal as part of the power and control circuit. Of course it cuts costs and it also reduces weight a small amount. But the weight of 100 feet of ground wire is totally offset by the weight of one power-seat adjusting mechanism. So it all gets down to priorities and cost reductions.

So you want to go back to the old VW way of wiring? Where everything has both a feed and a ground wire? There is nothing inherently wrong with using body metal as a ground path, it works. And adds no weight to the vehicle, but it needs to be done correctly.

 

One advantage I see using wires for ground instead of chassis for ground is that you don't have to deal with that pesky corrosion problem. However, I've never worked on a VW and I seem to remember they had wiring issues. But that was back in the 60's and 70's.

@Back to school There have been times I could have sworn I understood something a certain way only to discover I either learned it wrong or remembered it wrong. I believe there's no shame in being wrong or admitting it. In fact, I'd rather say "I was wrong" or "I don't know" than to try to give a factual answer that is in error. Answering when one doesn't know the answer is the fastest way to look foolish (for me). Not saying you were foolish, only that I (we) disagreed with your assessment of the term "Bad ground". Believe me - I've made a LOT of mistakes here on this forum. But I've learned from them.

Glad you've come to a better understanding of the topics we've discussed. Now - Stay Healthy.

 

This whole thread is based on a problem that has come about over the years, Modules controling many things or even most things. When a single circuit is resposable for something working or not, it's fairly easy to find the problem. But when one computerized module controls many things it gets harder and harder to find the real problem. Many of the things in a module share a ground rail, so when a ground is found one place it MAY allow something else to function.

That above is why I never work on Ford products now, and I grew up hating GM and loving Fords. Ford has a module now for everything and many are far away from what they control. Think about a while back with #12 and his Ford Exploder, his problem was finally solved but wasn't what he expected. My oldest son had an Exploder and while he lives far from me we tried to diagnose his problem. And in the end he had to get rid of it, talked him into getting a Chevy and he can't believe how much easier things are to maintain and work on compared to Fords.

Yes, modules control almost everything today. Not looking to debate this but there's very little difference between Ford and GM Can Bus systems. Most if not all systems actually related to driving all use mandated protocols based on the current Bosch CAN Bus design. None driving systems is where they differ. Things like the entertainment system although that's changing with what's happening with the ability to remotely take control of vehicles through the entertainment system. Another example is with electric steering. Manufacturers took away the ability to access the steering characteristics before it was mandated. It could be also mandated now? I don't know. There are some non-Bosch systems but they are few and far between. The one thing GM does have going for it that simplified their CAN systems was with sticking with push rod engines. Much less complicated meaning they are less sensor dependent. That makes a huge difference in the amount of traffic on the CAN.

 

there's very little difference between Ford and GM Can Bus systems. Most if not all systems actually related to driving all use mandated protocols based on the current Bosch CAN Bus design. None driving systems is where they differ.

US domestic cars (ford, gm, chrysler) didn't really start using CAN til about 2006. Before that they all used different types of protocols. Most all where single wire and much slower but for someone working on cars these "data lines" are all pretty much the same thing tho so no reason to get much into details about it.

The newer cars these days all have like 3-5 different communication systems in them now. No longer is it just one pair of CAN Hi & CAN Lo.

 

Yes, modules control almost everything today. Not looking to debate this but there's very little difference between Ford and GM Can Bus systems. Most if not all systems actually related to driving all use mandated protocols based on the current Bosch CAN Bus design. None driving systems is where they differ. Things like the entertainment system although that's changing with what's happening with the ability to remotely take control of vehicles through the entertainment system. Another example is with electric steering. Manufacturers took away the ability to access the steering characteristics before it was mandated. It could be also mandated now? I don't know. There are some non-Bosch systems but they are few and far between. The one thing GM does have going for it that simplified their CAN systems was with sticking with push rod engines. Much less complicated meaning they are less sensor dependent. That makes a huge difference in the amount of traffic on the CAN.

Quite a few years back I interviewed for a job as the lead engineer at a company developing electrical power steering systems. I did not take the job, the 45 mile commute was daunting. But I think that product is in use in a few vehicles even today. Totally electric steering, especially under computer control, is a fearful concept, given the reliability of automotive systems, and the poor quality of big computer programs. And in this part of the country the HUGE amounts of salt dumped on the raods for several months of the year make corrosion a real concern. Road salt concentrations in road spray are far worse than ocean water, unfortunately.
And at a more recent job I did have to interface with the GM test system for some of their production line testing. The problem at that time was that none of the actual code matched any of the available documentation, and so the communications lines only got checked for shorts and opens. The biggest advantage of using the communications bus in cars is that it can keep the aftermarket competition out.

 

The biggest advantage of using the communications bus in cars is that it can keep the aftermarket competition out.

I'm not too sure of the validity of this statement. There is a massive amount of aftermarket support across the board. In fact I prefer many aftermarket solutions to their oem counterparts which can be quite limiting sometimes.

 

The one thing I'm sure of about CAN is this, for something that is always referred as having the benefit of simplicity, it's awfully complicated. Yes it is a multiplexed network with channels containing mandated standardized messaging protocols for overall vehicle communication and there are channels that are for proprietary manufacturer defined specific messaging. I believe channels have also already been dedicated and defined for autonomous driving.

SAE J1939 was first released in 1994 to standardize CAN for vehicles. It is something that is constantly being revised and updated. Starting in 2000, SAE 1939 was updated to where CAN and the J1939 protocols became mandatory in all vehicles sold in the US. Mandatory implementation did have a generous lead time for a regulatory mandate. Off hand I don't remember what the due date for implementation was but 2006 sure sounds about right. IIRC CAN mandates did exist before this for emission monitoring and control.

 

I'm not too sure of the validity of this statement. There is a massive amount of aftermarket support across the board. In fact I prefer many aftermarket solutions to their oem counterparts which can be quite limiting sometimes.

Yes, this is primarily from the impact of the EU passing what they called blocking legislation. As far as the CAN goes, it forced open sourcing for non-proprietary channels. Another aspect had to do with parts. Manufacturers were required to offer repair or service parts for "X" amount of years following the end of a production model. Particularly in Europe it was the practice to sell the rights to produce the service parts. The blocking laws did away with that where anyone can make service parts. It did come with the restriction that non-genuine parts couldn't claim to be genuine. Considering something like the price of a Mercedes fender, these changes made a big difference in the cost of repairs and in most of Europe you can't drive a damaged car. They fail inspections. US manufacturers universally accepted the legislation instead of trying to produce two different versions of the same cars based on where they were sold.

 

The biggest advantage of using the communications bus in cars is that it can keep the aftermarket competition out.

Manufacturers still have their dedicated proprietary channels on the CAN. For example, the GM OnStar and Ford Sync systems. Unlike your phone there aren't a lot of APPs available for the systems. Access to the systems isn't free and requires final approval from GM or Ford. So in some ways you're right on. Whereas somebody like Edelbrock developing high performance engine parts, manufacturers can't prevent that from happening.

 

In the US, everything is driven by Corporate Average Fuel economy Average or commonly called CAFE numbers. Each manufacturer reports the number of each model sold, representing MPG of each. High MPG vehicles sell more in most years, lately it been trucks & SUV’s. If they go over the average, they are fined by the DOT $100,000 per mile per gallon over. They have a strong incentive to reduce weight from smaller wires, more control modules, electric steering, aluminum and SCM’s in the body. The wiring harness is a huge expense as most models, each sub-harness is assembled on a board with holding clips and interestingly project a light onto the board for each color of wire and its route. Terminals attached, connectors installed then tested before wrapping, clip, harness tray guides and all. If it passes only then it gets a tape for plant, shift, date code and part number. Splice-packs are used to bring multiple grounds together and used for serial data lines for diagnostics. Class-2 is cavity 2 on the OBD-II connector. Scan tool installed, comb removed from the splice-pack connector, jumper wire installed from terminal to class-II cavity, you see if you can communicate with that model. If not, then the wire is checked, terminal pin fit checked, power and ground established or the model is replaced and programmed. Wires joined together in the harness are “Spot Welded”, no solder, no crimped steel which is quicker than the old methods.
In our rust belt in the upper Midwest, I use dielectric grease by the tube to grounds, connectors, anything in the engine compartment and all exterior light bulbs. This keep moisture, galvanic action and corrosion. I was service manager at a boat dealer with 8 techs, 13 lines of product and premium fiberglass line was “Sea Ray” up to 34 foot. So the Mercury tubes of dielectric grease where huge and required everywhere.
Voltage drop was used to test the cranking solenoid key circuit. The engine package comes assembled and know idea what boat they where installed. The key could be 34 feet away on a 24 foot boat and grounds everywhere. Any metal item that passes thru the hull plus the stern drive had two grounds to provide a path for sacrificial anodes could work.
Voltage drop, dielectric grease and grounds where important as there is no metal frame for negative.
In Europe, many vehicles has positive ground electrical systems, I could understand laws maybe implemented.
I just learned decades ago when diagnosing an electrical problem, especially intermittent problems, was to not disturb components, harness or anything else as much as possible. I have seen batteries cause strange problems as well as alternators. This is why I check voltage drop from the case to battery ground, and quickly test A/C voltage for a bad diode. A fused jumper wire on a dedicated circuit like an electric fuel pump, using the primary circuit side of the huge engine analyzer in shop in the 70’s & up, would show a normal up-down smooth wave form as the brushes made and broke contact with the commentator plates of the armature. The amperage tells you a lot as you got used to seeing what’s normal. Good pattern, but high current=restricted fuel filter, low current comes with a goofy pattern= worn out pump. Yes a scan tool is required on vehicles going back to 1992. But it is written into the diagnostic flow chart. I looked at a BCM used in a 2003 Tahoe and switched to ground to control 31 items, but the module had only 1 chassis ground. Modules operating with less system voltage or high resistance on chassis grounds operate funny and often find ground elsewhere creating problems described in the original post that started this thread. I use what works for me, but there are some common truths regardless of vehicles.
Just remember that if one circuit inoperative is isolated to the power & ground path diagnostic test on that circuit. If multiple circuit failures are confirmed, then start with the battery & distribution point.