I have a 1997 GMC Suburban k1500 (5.7L). When taking it in for its bi-annual emission test, it failed the test due to a message from the computer dealing with the oxygen sensors stating that it was a non-supported function. The garage that's working on the vehicle reflashed the computer thinking the programming had gotten messed up with no luck. They did manually check and found (2) malfunctioning oxygen sensors. One non-working and one with real slow response. But they stated that would result in the computer saying that it was a non-supported function. They supposedly called the gmc tech desk as well as the emissions tech desk and no one could figure it out. They now want to replace the entire PCM. Does this seem legitimate?
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Re: Not supported function with PCM
I suggest instead of getting entire PCM replaced you may please swipe your GMC 1997 GMC Suburban K 1500 with another latest version. Because the replacement will cost you a lot and there is no warranty or guarantee that the Suburban will function normally after the entire PCM replacement.
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Retarding the timing will cool the combustion which will lower the Hydrocarbon number,it will run bad but after a passed e test put the timing back to an advanced state which may help with the stumble.
Jose, I don't know if this will give you the answer you are looking for because there are many things to consider here. The exhaust gas recirculation valve (EGR) is one of the main things involved in reducing NO emissions. This valve is controled by the power control module. (PCM) This is your vehicles computer. The PCM monitors the vehicles speed and will command the EGR to open when the vehicle attains a certain speed, which is why the ASM test being done is recorded at two different speeds. At 25 MPH your vehicle failed the hydrocarbon (HC) emissions limit and this could be for a number of reasons. When is the last time you car was tuned up? Old spark plugs, wires, clogged air filters, oxygen sensors, leaking injectors (personal experience) or the PCV valve could be contributing to the results of the test. I guess that the easiest way to go is to tune up the engine replacing the spark plugs, wires, air filter and the PCV valve and don't forget to have the oil changed at the same time. Only then should have the vehicle retested and see what the results are. Should it fail again you may have to consider having the EGR or the catalytic converter replaced depending on what portion of the test fails. If the NO fails I would consider the EGR. If the HC fails then I would consider the catalytic converter. Good luck with this.
EVAP Control System Canister Vent Solenoid Circuit Malfunction
The EVAP system monitors the canister vent (CV) solenoid circuit for an electrical failure. The test fails when the signal moves outside the minimum or maximum allowable calibrated parameters for a specified canister vent duty cycle by PCM command.
Symptoms: You will likely not notice any drivability problems.
Causes: A code P1451 may mean that one or more of the following has happened:
*VPWR circuit open *Damaged canister vent solenoid *Canister vent solenoid circuit open or shorted to ground, power, etc. *Damaged Powertrain Control Module (PCM) *Possible SolutionsVerify canister vent solenoid - To verify normal functioning, monitor the EVAP canister vent solenoid signal PID EVAPCV and the signal voltage (PCM control side).With the valve open, EVAPCV indicates 0% duty cycle and a voltage approximately equal to battery voltage. When the valve is commanded fully closed, EVAPCV indicates 100% duty cycle, and a minimum voltage drop of 4 volts is normal. Output test mode may be used to switch output on/off to verify function. *Replace canister vent solenoid
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