Automobile Relay Repair, Schematic

Thread Starter

MrAl

Joined Jun 17, 2014
9,641
Hello there,

Recently i had quite a bad experience with my Volvo and i had to get towed home from the supermarket.
It appears that the problem could very well be the fuel pump relay. This is not really a relay alone though it is a controller of sorts. It has a relay in it, but also a complicated circuit that decides when to turn the relay on and off and is signaled by the ECU.

What i really need is a schematic. I've been going nuts the past several days trying to draw a schematic by tracing out the board but it's very difficult because there are many SMD parts and some of the traces go under the IC chip which is also a 16 pin SMD part so i cant see under the chip.

The part number is 9434225.

Any ideas would be great. I've already spent hours on this trying to draw up the schematic and still have hours to go.
I didnt want to buy a new one yet they are rather pricey but also wanted to try to find out exactly what was wrong so i know what it was. I already found a few design flaws, but they are not the cause of this problem.
 

Dodgydave

Joined Jun 22, 2012
10,592
You won't get a diagram of this online, you're going to try and reverse engineer it , with smd stuff and dual sided circuit boars these are next to impossible.
If you're sure its the pcb that's the cause just get another one.

Post pictures of the circuit board
 
Last edited:

LowQCab

Joined Nov 6, 2012
2,670
Bosch is infamous for their "Special-Relays",
but they're actually quite reliable.
Your original probably survived for ~30+years,
just buy a new one, they're still available.

If there are no "special" extra Pins on the bottom,
just try a standard Bosch-Relay without the built-in Timer.
Or try it even if it does have the extra Pin, it won't hurt anything.
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Thread Starter

MrAl

Joined Jun 17, 2014
9,641
You won't get a diagram of this online, you're going to try and reverse engineer it , with smd stuff and dual sided circuit boars these are next to impossible.
If you're sure its the pcb that's the cause just get another one.

Post pictures of the circuit board
Believe me it wont help to see the circuit board :)

Yes it is always possible to get another one i guess. I was hoping to find out what the problem was though, and it may not actually be the relay at fault.
 

Thread Starter

MrAl

Joined Jun 17, 2014
9,641
Bosch is infamous for their "Special-Relays",
but they're actually quite reliable.
Your original probably survived for ~30+years,
just buy a new one, they're still available.

If there are no "special" extra Pins on the bottom,
just try a standard Bosch-Relay without the built-in Timer.
Or try it even if it does have the extra Pin, it won't hurt anything.
.
.
.
Not sure what you mean. This relay is not just a relay it is a controller too. The controller gets signals from the ECU and then reacts in the way it should according to the design of the circuit. The circuit has 25+ parts on it including resistors, diodes, capacitors, etc.
I doubt that the ECU could drive a relay coil by itself if that is what you are suggesting.
 

LowQCab

Joined Nov 6, 2012
2,670
It would really help to have a Schematic.
I suppose this could be some type of special "Controller" that someone though would
be a good idea to stuff into a Relay-Case, that I've never seen,
but Timer-Relays from Bosch are very common in '80's/'90's European Cars.

Special Bosch Relays in older Volkswagen and BMW cars are simple Timers.

This being a Fuel-Pump-Relay means that it is designed to turn-off the Fuel-Pump,
if the Ignition remains "On" for more than a few seconds, without the Engine running.
This, of course, could also be handled internally by the ECU,
but back in the day they did some strange things.
So the Circuitry could be an "Engine-Running-Detector" of some sort.

This type of Fuel-Pump shut-off functionality was common
with Bosch "K-Jetronic" "CIS" style Fuel-Injection, ( which was largely mechanical ).

There may also be a special Relay for controlling the "Warm-Up-Enrichment-Injector",
( there's only one WUE-Injector mounted on the end of the Intake-Plenum ).

Automotive ECUs are used to drive all kinds of Loads,
various Relays would be a common usage.
( they directly drive ~4-Ohm Fuel-Injectors, and a few drive the Ignition-Coils directly )
.
.
.
 

debe

Joined Sep 21, 2010
1,324
Are you sure its the Relay/controler? First test i would do is feed 12V directly to the fuel pump & see if it actualy runs. Pumps do wear out the commutator long before the brushes, ive dismantled a few that stopped working just to see why they stopped working. They were Bosch pumps. Fuel pumps with worn commutators generaly start to sound noisy before they actualy fail.
 

Thread Starter

MrAl

Joined Jun 17, 2014
9,641
Are you sure its the Relay/controler? First test i would do is feed 12V directly to the fuel pump & see if it actualy runs. Pumps do wear out the commutator long before the brushes, ive dismantled a few that stopped working just to see why they stopped working. They were Bosch pumps. Fuel pumps with worn commutators generaly start to sound noisy before they actualy fail.
Well the problem is intermittent. The car runs fine, then when i come out from the store i start it, drive 10 feet, and it stalls and wont start. Then a half hour to maybe 45 minutes later the car starts again and runs fine again. So it's hard to believe it could be the fuel pump but stories on the web say it could be the relay. I guess it could be the pump but i couldnt test it because it's intermittent.

I dont want to just keep replacing things until it is fixed.
 

Thread Starter

MrAl

Joined Jun 17, 2014
9,641
It would really help to have a Schematic.
I suppose this could be some type of special "Controller" that someone though would
be a good idea to stuff into a Relay-Case, that I've never seen,
but Timer-Relays from Bosch are very common in '80's/'90's European Cars.

Special Bosch Relays in older Volkswagen and BMW cars are simple Timers.

This being a Fuel-Pump-Relay means that it is designed to turn-off the Fuel-Pump,
if the Ignition remains "On" for more than a few seconds, without the Engine running.
This, of course, could also be handled internally by the ECU,
but back in the day they did some strange things.
So the Circuitry could be an "Engine-Running-Detector" of some sort.

This type of Fuel-Pump shut-off functionality was common
with Bosch "K-Jetronic" "CIS" style Fuel-Injection, ( which was largely mechanical ).

There may also be a special Relay for controlling the "Warm-Up-Enrichment-Injector",
( there's only one WUE-Injector mounted on the end of the Intake-Plenum ).

Automotive ECUs are used to drive all kinds of Loads,
various Relays would be a common usage.
( they directly drive ~4-Ohm Fuel-Injectors, and a few drive the Ignition-Coils directly )
.
.
.
Well i am not sure what you mean by a 'timer' here. But yes you are right, it's an engine detect relay that will turn off the pump if the engine is not running for some reason. This helps if there is an accident and there is a fire the pump stops pumping gas to the engine.

The ECU may be able to handle larger loads like 5 amps, but i have no way of knowing that and i dont know what kind of signal it sends to the controller relay (this relay). It may be designed for only 100ma or even less, so far the circuit shows it drives resistors only that in turn provide signals to the monostable one shots (2 of them). So as it normally is, it has very light load here, at least on that one signal line output from the ECU. Maybe it drives other relay coils directly, but not this one.
 
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