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Hello guys! my C5 it's been acting funny since the day I bought it, about a year ago or a little less but lately it's been worst, when I first start it on the morning is hard to rev and when I press the gas pedal it looks like it want to stall (sometimes it does) and sometimes stalls even if I don't press the gas pedal, when I accelerate hard it looks like it cuts the power and it does not accelerate like it should.
After the 14 sec, I try to rev the engine and just want to stall, I stopped from trying to rev and stabilized itself, after thar I tried harder to rev the engine.
Here is a video of this morning:
I pulled the codes using the DTC:
PCM P0856 H C
PCM P2068 H C
TCS NO COMM.
SDM U1040 HC
Please help me diagnose this C5.
I'm guessing fuel pump but what do I know?
Hello guys! my C5 it's been acting funny since the day I bought it, about a year ago or a little less but lately it's been worst, when I first start it on the morning is hard to rev and when I press the gas pedal it looks like it want to stall (sometimes it does) and sometimes stalls even if I don't press the gas pedal, when I accelerate hard it looks like it cuts the power and it does not accelerate like it should.
After the 14 sec, I try to rev the engine and just want to stall, I stopped from trying to rev and stabilized itself, after thar I tried harder to rev the engine.
Here is a video of this morning:
I pulled the codes using the DTC:
PCM P0856 H C
PCM P2068 H C
TCS NO COMM.
SDM U1040 HC
Please help me diagnose this C5.
I'm guessing fuel pump but what do I know?
What year is the car ??…P0856 doesn’t look familiar and no “P” or Powertrain DTC’s start with a P2XXX…power train codes are all P1XXC or P0XXX that I’m familiar with…you will need a scan tool at minimum to diagnose this.
What year is the car ??…P0856 doesn’t look familiar and no “P” or Powertrain DTC’s start with a P2XXX…power train codes are all P1XXC or P0XXX that I’m familiar with…you will need a scan tool at minimum to diagnose this.
Is a 2004, I searched for the code P0856 on google and there are several threads here at corvetteforum about other users having this code.
The onboard computer displays this message everytime I start the car: Service Vehicle Soon
Ok, for an 04 this is the DTC…do you have a factory level or equivalent aftermarket scan tool ??…I’d first erase the code and see if it comes back…if you don’t have scan tool a DVOM with a frequency function will be needed…checking for 5 volts from that circuit which comes from the PCM going to the EBCM can be checked too…when I had my C5 it would throw a similar code (P1644) occasionally but it was generally a nuisance code…under certain conditions that code would cut off some injectors.
Ok, for an 04 this is the DTC…do you have a factory level or equivalent aftermarket scan tool ??…I’d first erase the code and see if it comes back…if you don’t have scan tool a DVOM with a frequency function will be needed…checking for 5 volts from that circuit which comes from the PCM going to the EBCM can be checked too…when I had my C5 it would throw a similar code (P1644) occasionally but it was generally a nuisance code…under certain conditions that code would cut off some injectors.
Thank you for your answer, I have no experience checking this kind of fails on cars but I do have a multimeter that test for frequency and duty cycle, I'll try to check this first.
Interesting video. When I was having starting and engine dying issues while driving 6 months ago, my go to mechanic diagnosed the issue as a bad ignition switch. He replaced the switch (took the 4th one to work-China crap!) and have had no further problems.
...bad ignition switch. He replaced the switch (took the 4th one to work...
That sounds incredibly hard to diagnose. How the heck would you change the ignition switch three times and still conclude the problem didn't lie elsewhere, your brand new parts were bad?
That sounds incredibly hard to diagnose. How the heck would you change the ignition switch three times and still conclude the problem didn't lie elsewhere, your brand new parts were bad?
He put one in, tested and did not work. He put the second one in. Again did not work and the same with the 3rd. The fourth one finally worked. All were new and came from GM.China crap.
Last edited by rrwirsi; Oct 4, 2024 at 01:11 PM.
Reason: spelling
Interesting video. When I was having starting and engine dying issues while driving 6 months ago, my go to mechanic diagnosed the issue as a bad ignition switch. He replaced the switch (took the 4th one to work-China crap!) and have had no further problems.
Did you have any other problems with the switch to really know it was the switch?
Did you have any other problems with the switch to really know it was the switch?
At home when the starting motor would not turn on to start the car, I tried my other two keys and no 'love'. Then I squirted CRC Mass Air Flow Sensor Cleaner in the ignition and the car started. Took a drive and the car ran good for about 3 miles then quit driving 70mph on 95. Luckily I carried the CRC with me, squirted some more and jiggled the key in the ignition and got the car started again. Took the C5 to my go to Mechanic and he replaced the ignition switch. I now carry a can of CRC in the car in case 'Murphy's Law' appears again.
At home when the starting motor would not turn on to start the car, I tried my other two keys and no 'love'. Then I squirted CRC Mass Air Flow Sensor Cleaner in the ignition and the car started. Took a drive and the car ran good for about 3 miles then quit driving 70mph on 95. Luckily I carried the CRC with me, squirted some more and jiggled the key in the ignition and got the car started again. Took the C5 to my go to Mechanic and he replaced the ignition switch. I now carry a can of CRC in the car in case 'Murphy's Law' appears again.
My car starts everytime I try, I have never experienced your car symptoms, It's just hard to rev when cold and sometimes stalls or want to if I don't give it a little gas to prevent from stalling when I'm on a light or in stop sign.
Hello again guys, I want to test for Hz, duty cycle and voltage at the EBCM connector, but I can't find a way to remove it, I raised the gray handle and pulled and wiggled the connector but it does not come loose, any recommendations?
Hello guys, after trying several things to fix the problems (clean the grounds, try to take readings on connectors, clean the intake) I took the switch out and cleaned the contacts like in this post: https://www.corvetteforum.com/forums...ch-repair.html
All the problems that had the car to rev when cold and stalling sometimes are gone!, I'm still having the same codes: PCM P0856 H C PCM P2068 H C TCS NO COMM. SDM U1040 HC
But if you are experiencing some weird problems on your C5 I can't recommend more a solution! try this one and is not that hard to do it.
Hello guys, after trying several things to fix the problems (clean the grounds, try to take readings on connectors, clean the intake) I took the switch out and cleaned the contacts like in this post: https://www.corvetteforum.com/forums...ch-repair.html
All the problems that had the car to rev when cold and stalling sometimes are gone!, I'm still having the same codes: PCM P0856 H C PCM P2068 H C TCS NO COMM. SDM U1040 HC
But if you are experiencing some weird problems on your C5 I can't recommend more a solution! try this one and is not that hard to do it.
Tom
It's a temporary fix. Seriously, if you are going to all that trouble to remove a 25 year old ignition switch...just replace it. They are readily available. Only $100 for genuine GM.
It's a temporary fix. Seriously, if you are going to all that trouble to remove a 25 year old ignition switch...just replace it. They are readily available. Only $100 for genuine GM.
Yeah! probably it is a temporary fix but now I know that it is the switch that is causing the trouble, if it start to fail again down the road, I will replace it with this one: https://www.rockauto.com/en/moreinfo...=4700&jsn=1315 from RockAuto
C5 hard to rev when cold
