Isuzu Trooper Gravity sensor failed and cant get one, but have idea to replace it

Thread Starter

sdowney717

Joined Jul 18, 2012
648
Please tell me if my idea will WORK, I include a wire schematic for the G sensor.

I have looked at the factory service manual wiring schematic, and it looks like it is a simple variable resistor divider can be used to replace it. The sensor is designed to detect bumpy roads
The output voltage back to PCM is supposed to be between 2.35 to 2.65 vdc for normal operation.
Reference voltage is 5vdc
Ground is well ground turned on by PCM

I am thinking use a 500 ohm pot and set the voltage to middle or 2.45vdc for the detection wire feeding back to the PCM
The amp load for 5vdc with a 500 ohm resistance from ref to gnd is 0.01 amps, so I doubt the PCM would have an issue with that low amps?

Here is a description of how it functions

The G-sensor is also known as the Rough-Road sensor. (1996 Trooper)96 Trooper-G-sensor-big.png

From Alldata.com:

The Gravity (G) sensor is a vertical Low-g (gravity) acceleration sensor. By sensing vertical acceleration caused by bumps or potholes in the road, the powertrain control module (PCM) can determine if the changes in crankshaft speed are due to engine misfire or are driveline induced. If the G sensor detects a rough road condition the PCM misfire detection diagnostic will be deactivated. The G sensor at rest output should be between 2.35 - 2.65 volts (+1G). During a rough road condition the voltage output can vary between 0.5 volt (-1G) and 4.5 volts (+3G).
 
Last edited:

Picbuster

Joined Dec 2, 2013
979
Please tell me if my idea will WORK, I include a wire schematic for the G sensor.

I have looked at the factory service manual wiring schematic, and it looks like it is a simple variable resistor divider can be used to replace it. The sensor is designed to detect bumpy roads
The output voltage back to PCM is supposed to be between 2.35 to 2.65 vdc for normal operation.
Reference voltage is 5vdc
Ground is well ground turned on by PCM

I am thinking use a 500 ohm pot and set the voltage to middle or 2.45vdc for the detection wire feeding back to the PCM
The amp load for 5vdc with a 500 ohm resistance from ref to gnd is 0.01 amps, so I doubt the PCM would have an issue with that low amps?

Here is a description of how it functions

The G-sensor is also known as the Rough-Road sensor. (1996 Trooper)View attachment 187285

From Alldata.com:

The Gravity (G) sensor is a vertical Low-g (gravity) acceleration sensor. By sensing vertical acceleration caused by bumps or potholes in the road, the powertrain control module (PCM) can determine if the changes in crankshaft speed are due to engine misfire or are driveline induced. If the G sensor detects a rough road condition the PCM misfire detection diagnostic will be deactivated. The G sensor at rest output should be between 2.35 - 2.65 volts (+1G). During a rough road condition the voltage output can vary between 0.5 volt (-1G) and 4.5 volts (+3G).
https://www.autozone.com
https://www.autohausaz.com/isuzu-auto-parts/isuzu-trooper-parts.html

picbuster
 

Thread Starter

sdowney717

Joined Jul 18, 2012
648
Again, you can not buy it anymore, I also looked at your links, there is no listing.
They have dropped all support for this sensor.
A lot of places will not pass your car if it shows an engine code.
https://www.autohausaz.com/catalog/k/isuzu/1996/1340~96~210~1~~5~8-trooper_ls/g sensor?s=r&page=3

Sensor part #8-p7115-937-0 is an oem unavailable part only.

Discontinued parts cant be bought.
https://www.alldiscountparts.com/oem-parts/acura-sensor-acc-road-8971159370

Further info shows that part number is used on the Trooper and Honda and maybe others, but cant buy one anymore.
https://www.planetisuzoo.com/viewtopic.php?f=1&t=16680
 
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jpanhalt

Joined Jan 18, 2008
8,116
Your solution sounds workable, if the total resistance of the pot is approximately what the sensor's resistance was. However, if your concern is not getting an engine code, wouldn't a fixed voltage there be likely to give a "misfire" code if you drove over rough roads? You might want to set it to the "bumpy road" voltage.

What is the present sensor showing as a code?
 

Thread Starter

sdowney717

Joined Jul 18, 2012
648
Your solution sounds workable, if the total resistance of the pot is approximately what the sensor's resistance was. However, if your concern is not getting an engine code, wouldn't a fixed voltage there be likely to give a "misfire" code if you drove over rough roads? You might want to set it to the "bumpy road" voltage.

What is the present sensor showing as a code?
P1392 code. I will have it scanned again.
If you set it outside that volt range, and volts are maintained too many seconds, it will throw a code.
Sensor had been sending back 4.5v as if Trooper was on a very bumpy road all the time, like it was internally stuck, so when I whacked it, sensor then sent 0.5v which is too low.
If this G sensor goes outside normal range, ECU will start checking crankshaft timing more aggressively for misfires as a real bumpy road could affect the rotation of the crankshaft or something like that. If voltage is sitting too long at an unexpected number, it throws a code.
This is a silly over engineering example as cars back then unless they were high tech racers did not have such things.
Here are Isuzu codes, you can see intermittent codes are showing too, which is like the sensor is sticking.
Is it possible if the ECU never detects voltage change it could throw a P1391? But that might take a while?

Thing is, if you disconnect the battery, the ECM codes get reset, but for how long, not sure.

Somehow sensor is able to change resistance as it is bounced up and down, is it mechanically balanced inside? or purely electronic?
Is there some other electronic device I could substitute to replace its functionality?
Read more at: https://www.obd-codes.com/trouble_codes/isuzu/

P1390 G Sensor Circuit Intermittent Voltage Low
P1391 G Sensor Performance
P1392 G Sensor Voltage Low
P1393 G Sensor Voltage High
P1394 G Sensor Intermittent Voltage High
 
Last edited:

jpanhalt

Joined Jan 18, 2008
8,116
From original post:
From Alldata.com:

The Gravity (G) sensor is a vertical Low-g (gravity) acceleration sensor. By sensing vertical acceleration caused by bumps or potholes in the road, the powertrain control module (PCM) can determine if the changes in crankshaft speed are due to engine misfire or are driveline induced. If the G sensor detects a rough road condition the PCM misfire detection diagnostic will be deactivated. The G sensor at rest output should be between 2.35 - 2.65 volts (+1G). During a rough road condition the voltage output can vary between 0.5 volt (-1G) and 4.5 volts (+3G).

I figure its better to not have a misfire detector than one that detects misfires when there are none.
 

Thread Starter

sdowney717

Joined Jul 18, 2012
648
I had it scanned again and verified the p1392 code.
I will get it inspected, maybe it will pass. If not I will try the potentiometer.

I did find out the YAW sensor also has a gravity sensor in it, the YAW sensor uses 4 pins, the gravity sensor 3 pins, they both likely work on the same 5v and similar principles. Does anyone have a circuit diagram and pinout of a YAW sensor?
Here is one
https://www.amazon.com/2009-2017-Nissan-Gravity-Sensor-479311EA1A/dp/B07NS6X5C7
 
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Thread Starter

sdowney717

Joined Jul 18, 2012
648
It passed Virginia state inspection, so pressure is off. I will eventually look into trying the pot idea.
If it works, I will cut open the old sensor, gut it ,and put the pot inside and seal it up.
 
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