Pontiac G6 Forum banner
1 - 6 of 6 Posts

·
Registered
Joined
·
6 Posts
Discussion Starter · #1 ·
I have an 09 G6 that says Engine power reduced and the error code it gave was P2127 I think and it said gas pedal sensor/ throttle position sensor bad. So I changed the pedal, then the Trottle body sensor, cleaned the throttle body and more general maintenance only to have none of that work. Now it throws the same 2127 error code but says APP circuit low now. Apparently the previous owner cut a bunch of wires and didnt connect back right so my uncle, a long time certified mechanic, fixed what he could but now thinks maybe bad wiring and no ground or something like that burned the computer up. Has anyone else ever had a similar issue? If I have to get a whole engine wiring harness it's not even worth keeping the car. Please Help lol!
 

·
Registered
Joined
·
5 Posts
Hi,
I have a 2008 G6 and also have intermittent issues with P127/ P128. I have replaced the throttle pedal, cleaned the throttle body (it was clean) and still the issue persists.
I can drive hundreds of miles without an issue and then it rears its head again. To fix I shut the engine down and clear codes and back to normal. I have read that the issue could be a broken wire which goes open circuit intermittently.
Does anyone know where to start?
It appears that the wires attached to the left side of a heat sink in front of the left side of the battery have been connected together with butt connectors and I don't know if that was a fishing exercise to find the faulty wire or not. The car was bought off the lot and I didn't notice the bundle of connected wires when I purchased the car. Also the problem seems to occur only when ambient temps are high. Please help.
 

·
Registered
Joined
·
5 Posts
I had a similar problem with my son's 2009 GT with the 3.5L engine.

There was a fault with the APP circuit. The fault was a low voltage at the sensor. I do not recall the specific code. The ECM then puts the engine in limp mode with default computer settings controlling the engine. Acceleration is limited due to the missing sensor values. Traction control is deactivated along with any unnecessary functions.

There was a loss of the 5 Volt 2 source from the ECM. This feeds the throttle control and the pedal position sensor. (On some vehicles it may power the crankshaft sensor.)

There are two sources of the 5 volts to the APP sensor. 5V1 and 5V2, if either are missing then the ECM puts the car in limp mode.

What I found was a broken wire inside the insulation for the harness from the ECM to the X108 plug (Pin K) near the left fender under the hood. The way the wiring harness is installed keeps too much stress on the individual wires and they can be damaged. The wires have been looped into a nearly 180 degree bend. I repaired the broken wire to restore normal operation. Once the 5V2 is restored the ECM will clear the faults and allow normal engine operation.

A copy of the schematic shows only two places using the 5V2 source. I also have attached a copy of the throttle body connector. If the 5V2 is missing then it needs to be traced back to X108. The connectors to the ECM are not likely to be a problem.

I hope that this may help some one who is looking at this circuit for limp mode or APP issues.

Copies of the X108 locations will be attached for this problem. The schematics for the Engine Control and APP circuits is also attached. The pin locations and circuit connections for X108 and the throttle body are included.
 

Attachments

·
Registered
Joined
·
5 Posts
RazG6,
thank you very much for all the detail. I am leery of connecting the meter 5 v to ground from the ECM. Is there any issue of the possibility of damage to the ECM?
I have already installed a new GM throttle pedal and found the old pedal to be working ( after following testing procedure off the vehicle )
I purchased a rebuilt ECM and installed,but returned the unit as the seller said it was plug and play and it wasn't and I was not going to take it to the GM dealer to get the new ECM programmed.
As my issue is very intermittent (code p2138 only once this summer) approx. 6k's.I haven't done anything more. I will look at your very detailed attachments and may attempt some troubleshooting this winter as my G6 is a summer-only driver.
 

·
Registered
Joined
·
5 Posts
The XT108 plug is readily accessible as it is located under the top frame adjacent to the windshield washer reservoir. All of the power for the throttle actuator control comes through this plug. The power for the APP and TAC also comes through this plug. The plug is secured to the bottom of the frame by a push type retainer. It can be removed for easier access to take measurements and help isolate the problem.

This information is for the 3.5L engine and it is slightly different for the other engines in the G6.

I will attach a copy of the system description for the Throttle Actuator Control system.

When you have a reduced power condition there are three main areas to verify the proper voltages.

1) Accelerator Pedal (APP) assembly.
2) Throttle Body
3) ECM
The least likely problem would be the ECM.
 

Attachments

·
Registered
Joined
·
5 Posts
RazG6 thanks again for the help. I will look into the X108 connector and check the wiring. I hope to find something.
The Accelerator Pedal (APP) assembly. has been changed. The p2138 code still came back, only once during the summer [ hot ambient temperature and car ran fine after code was erased with a code reader.
I have done nothing since then. I keep looking at the wiring harnesses and disconnecting and reconnecting connectors to remove possible pin problems.
 
1 - 6 of 6 Posts
Top