05 TB won't start after head gasket replacement

[AirSick]

I'm new here and this is my first post. I recent purchased an 05 TB EXT with the 4.2. After a couple of days of driving we started having a over heating issue. Changed the thermostat thinking that was the problem but it still over heated occasionally. Had a buddy of mine do a leak down test just to make sure it wasn't the head gasket but unfortunately it was.

Long story short, before we pulled anything off we marked everything timing wise so we knew exactly where to put it back. Pulled everything apart, head was warped so had a machine shop shave it, put it all back together, lined up all timing marks and we were good to go.

Got ready to start it and nothing. Turns over, sounds good turning over just no fire. My buddy to it to his shop to put it on his diagnostic machine and it pulled up 2 codes. One was the lovely P060E code and the other he couldn't remember but knew it dealt with the TPS. We both are at a loss as to why it will not start.

Checked all connections, checked everything and all is good. Any help would be greatly appreciated before i take it to the dealer and get reamed a new one.

 

[gmcman]

Need to know the other code.

Did you rotate the engine 3 times before buttoning it up and ensure the timing marks stayed in time?

Are you getting fuel? Does the pump energize when the key is turned on?

Did you perform the TB relearn?

Pull a plug and crank the engine and see if a fuel odor comes through the spark plug hole.

 

[Mooseman]

The P060E code is associated to REP which is usually caused by a problem with the Throttle body or the pedal sensor. Although the following link is for a V8, they work on the same principle: New Throttle body??? - Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum

The other code may be the key to exactly what is going on. Either the TB or the pedal sensor is affected.

 

[AirSick]

Come to think about it, this had to have been flooded once before. For the month or so it sat at my buddys garage it did develop mold on the carpet pretty bad. Could that have effected the pedal sensor in some way?

 

[Mooseman]

Could be possible. Instead of shotgunning with a new part (~$100), try to find a used one. Maybe grab a TB while you're at it if it's a U-Pull-It type yard. Should be fairly cheap that way.

 

[AirSick]

I did talk to my mechanic today about the pedal sensor and he said it was getting good voltage to it. Would the throttle body cause this thing not to start? Hes going to double check the pedal sensor again on Thursday, along with double checking the injectors.

 

[The_Roadie]

The pedal assembly has TWO sensors. They are potentiometers, like volume controls. The PCM sends them 5V and ground, and then EACH sensor sends back a voltage that corresponds to the position of the pedal. One sensor sends back increasing voltage for a depressed pedal. The other one sends back a decreasing voltage for a depressed pedal. The PCM compares the behavior of these two outputs, and if they are inconsistent or if one is locked at zero or 5V while the other one moves, it assumes the pedal assy is bad and then it complains.

The throttle body has two identical kinds of sensors to report back to the PCM that the stepper motor in the throttle body has successfully moved the butterfly valve disk when it was commanded to move it.

 

[AirSick]

So lets just say if one of the sensors are bad. Would this keep it from running?

 

[The_Roadie]

It would reduce power and probably not let it go above idle. You'd have the REP light. I don't know at all if it suppresses the ability to start.

 

[Wooluf1952]

I don't know if the '05 is different, but on my '03 Envoy, I had something get lodged in the t-body holding the butterfly open. The pedal said the t-body should be closed an the t-body said WRONG. The engine died and would not restart until the item was removed.

 

[AirSick]

It has both the SES and REP light on. It cranks over nice, like it normally should just no fire. It gets spark, fuel pressure is right where its supposed to according to my mechanic.

To Wooluf, the butterfly plate is closed. Just wandering if the butterfly plate should move when you press the pedal.

 

[Wooluf1952]

It should move if the key is in the RUN position and you press the pedal.

 

[AirSick]

See mine has no movement at all.

 

[Wooluf1952]

Is it possible one of the wires got messed up during the head change?

 

[AirSick]

We made sure all of the wires were out of the way when we did the gasket change. Also made sure everything was marked to make sure it went back were it came from.

 

[Wooluf1952]

I'm out of ideas. Sorry.

 

[AtlWrk]

My buddy to it to his shop to put it on his diagnostic machine and it pulled up 2 codes. One was the lovely P060E code and the other he couldn't remember but knew it dealt with the TPS. We both are at a loss as to why it will not start.

The first step of troubleshooting the P060E code asks if other TPS related codes are present, and if so, to troubleshoot those first. Knowing what that other code is could save a lot of guesswork.

Given the amount of teardown and moving around of parts it wouldn't be unheard of to damage a harness in a subtle way (e.g. cracking a wire at the terminal in the throttle body connector).

It sounds like your PCM is having trouble commanding the throttle body. It should snap shut then release when you first turn the key to RUN (but not START). Does it not even do that?

 

[AirSick]

Come Thursday I will know what the other code is since thats the next day my mechanic is working. I never did think to check if the plate moves when the key is turned on. I just know it doesn't move when the pedal is pressed down. Sorry, I'm new to the computer controlling everything situation.

 

[Sparky]

Key has to be in the on position for the pedal to move the throttle blade. It won't do anything with the ignition turned to off or accessory.

 

[AirSick]

My buddy just said the plate does not move at all.even with the key in the on position.

 

[The_Roadie]

I would then check the 5V reference and ground at the TPS, and the signals coming out of the two sensors. Note that trying to move the butterfly plate while the power is on can burn out the stepper motor that moves it, assuming the sensors are working and the PCM has control over the stepper. Which may or may not be true for you.

 

[AirSick]

So some news from my buddy. He had already checked the 5v reference and ground everything good. Still no throttle plate opening though. Pulled the plugs to see if he could smell fuel, no fuel smell but has good fuel pressure. He was able to manually open and close the injectors but not sure if the computer is allowing them to.

 

[Sparky]

My impression is it is more likely to be an issue with the throttle body and/or the wiring to it since you had to remove all that to do the head gasket than the pedal which was not touched. I'd be analyzing every wire to it.

 

[The_Roadie]

So some news from my buddy. He had already checked the 5v reference and ground everything good.

Haven't heard if he also checked the sensor output wires. All the way back to the PCM.

Assume he's checked the fuse that powers the fuel injectors? And power at the injectors?

 

[AirSick]

The other code was P2101. hope that helps out some.

 

[Sparky]

P2101: Throttle Actuator Position Performance

That points to the throttle body also (though again could be wiring and not the throttle body itself).

If you were closer I'd stop by and look at it, swap your throttle body into my truck to make sure it is still working, etc... Anyone near you that you could do that test with?

 

[AirSick]

Unfortunately I don't think so. He did say when you turn the key to the on position the throttle plate does not move.

 

[AtlWrk]

You said he checked the 5V and ground references and they were good but what about the other wires? The throttle body is connected directly to the PCM (and only the PCM) with 8 wires. It should be trivial task to check the continuity of every single one of those wires between the throttle body connector and the C2 connector on the PCM. Has this been done?

I know if one of the feedback circuits is malfunctioning the engine will still start (in REP mode) but I suspect if the PCM detects it has no control over the throttle it won't let it start at all. This would be the case if one of the throttle actuator control (TAC) motor wires was broken.

What about checking every single fuse for continuity with a meter? There isn't a "throttle body" fuse per se but there are several PCM, ETC fuses that feed various subsystems in the PCM.

FWIW my money is still on an electrical issue rather than a coincidental throttle body or PCM failure.

 

[gmcman]

I would remove the TB harness and spray the contacts with electrical cleaner. Then I would pull the 3 ECM harnesses and ensure there are no bent pins and no dirt.

What about the cooling fan harness? Doesn't this coincide with the ignition switch? I don't remember how much the ignition switch controls but I remember the fan is tied into this 5V maze.

 

[AirSick]

Well my buddy has been looking at this thread so I guess he is going to try some of the things yall have mentioned tomorrow. I will give an update as soon as I hear from him.

 

[AirSick]

Well all pins are straight and clean, now broken or pinched wires. All fuses were checked and everything is good. Going to call one of my buddys at my local dealer and get his take on this thing.

 

[Mooseman]

If he can hook up a Tech2 to see exactly what is going on, can probably narrow it down real quick.

 

[gmcman]

Try unhooking the vacuum line from the side of the TB and see if it fires. May allow just enough air in.

 

[gmcman]

Need to know the other code. Confirmed

Did you rotate the engine 3 times before buttoning it up and ensure the timing marks stayed in time? Not confirmed

Are you getting fuel? Does the pump energize when the key is turned on? Confirmed

Did you perform the TB relearn? Not confirmed

Pull a plug and crank the engine and see if a fuel odor comes through the spark plug hole. Are the injectors connected?

Sorry but you didn't answer these for me.

Also, double check the cooling fan harness.

Did you disturb the crank sensor? If so, may need a CASE relearn. Check sensor lead.

You may have fuel pressure but the injectors don't sound like they are firing.

 

[Mooseman]

So far, the codes are pointing to the throttle body either being bad or the connector/wiring is affected. Has the throttle body been swapped? What about the pedal? You mentioned that it had been flooded once. That could be the cause as well. Since water normally never gets there, it's probably not water proof. If the signal is messed up badly, the PCM may not allow the engine to start at all as a safeguard. I'm still convinced it's one of these two that is causing this.

 

[AirSick]

To gmcman: we did turn the motor over and the marks stayed lined up. Fuel injectors are connected. Not sure if he did do the tb relearn.

 

[AirSick]

So far, the codes are pointing to the throttle body either being bad or the connector/wiring is affected. Has the throttle body been swapped? What about the pedal? You mentioned that it had been flooded once. That could be the cause as well. Since water normally never gets there, it's probably not water proof. If the signal is messed up badly, the PCM may not allow the engine to start at all as a safeguard. I'm still convinced it's one of these two that is causing this.

To my knowledge those 2 have not been swapped.

 

[gmcman]

I agree with Moose, the ECM is pretty reliable when telling us the faults. The fact the fuel pump is energizing tells one story, but no air and no injector along with the TB code surely points to either a faulty 5V reference (CHECK the cooling fan harness!) Not sure how it's tied into this but it is in some fashion. You may need a TB readaptation also. There is a procedure for checking continuity from the PCM to the TB, probing each wire but as Roadie stated, do not use a 12V test lamp!

 

[gmcman]

Do you remember if you disconnected the battery before you if not you cou

 

[gmcman]

because if not you could