Rough road G-sensor

5947 Views 3 Replies 3 Participants Last post by SARTrooper, Sep 6, 2003

SARTrooper

Discussion Starter · Sep 4, 2003

Sounds like looking for the G-spot on my Troop. Anyway...finally found a description of this code "P1391" which is referring to a "rough road G-sensor". Anyone know what the heck that is? And where? Since it is affecting my Check Engine light I would assume (there's that word) that it is associated with the vacuum system and the brake system in some way.
Or maybe it is my Troop's way of telling me to get out on some rough roads...

Help?
:roll:

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Canucklehead

· #2 · Sep 4, 2003

Circuit Description
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 crank- shaft 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 de-activated. The G sensor at rest output should be between 2.35 - 2.65 volts (+1G). During a rough road conditio, the voltage output can vary between 0.5 volt (-1G) and 4.5 volts (+3G).

Conditions for Setting the DTC

Engine running.
No vehicle speed.
G sensor signal indicates greater than 2.5 volts (+1G) or less than 1.5 volts (0G) for one minute.
-OR-
Vehicle speed is between 30 mph and 80 mph (50 km/h and 132 km/h).
G sensor signal changes more than .0002 volts each tenth of a second (changing faster than physically possible).

Not sure where it's located on a Trooper, but the replacement procedure seems like it would take about 5 minutes.

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Smiley

· #3 · Sep 5, 2003

Canucklehead said:
-OR-
Vehicle speed is between 30 mph and 80 mph (50 km/h and 132 km/h).
G sensor signal changes more than .0002 volts each tenth of a second (changing faster than physically possible).

Obviously, there must not be a G-sensor on the Subaru SVX...
Ain't that right, Mike?

Oh wait... UP TO 80mph...
NEVERMIND. :lol:

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~ 1997 Isuzu Rodeo S......... "THUD" ~ MUA5 | 3"+ 3" | 3.07s | OME HD Leaf Springs | MWM Rock Bars | Yellow 1-pc. Drive Shaft [> SOLD <]
~ 1995 Isuzu Trooper S....... "Heart of Gold" ~ MUA5 | 912s + 1" Spacer | 3.07s | 5.38s | 35x12.50s | ARB Bumper | Snorkel | Infinite Improbability Drive

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SARTrooper

Discussion Starter · #4 · Sep 6, 2003

First...where is the Rough Road G-Sensor? or is it a part of the PCM? Is it possible that an O2 sensor with a longer preheating time (in this case the Bosch OEM with a >15 second preheat time) could be causing this error code? I recently installed 2 of these in the aft-catalytic positions...but they have been (and still seem to be) working just fine. I have had increased performance and better gas mileage (~15-17 mpg city). It has only been after 4 weeks that I am now getting these error codes: P1391 X 2

I understand the Bosch Universal type has a shorter preheat time (<5 sec)...would these work better?

Thanks,
Rob
:roll:

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