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CNG not working, DTC P1215?

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  • CNG not working, DTC P1215?

    I have a 2001 Chevy Cavalier that has been having some problems with the CNG system. It won't switch over to NG, and the toggle switch on the dash won't show how much CNG is in the tank. A mechanic found that the low pressure solenoid had shorted out, but even after replacing it, it still didn't work. Now there's a CEL; pulled the code P1215 Ground Fault Detection Indicated. Something in the archive mentioned a Throttle Positioning Sensor, but would that cause the gauge not to show the tank level? Or something else instead is wrong?

  • #2
    Re: CNG not working, DTC P1215?

    some info on the trouble code:

    P1215MIL, High Pressure and Low Pressure Lockout Circuit Malfunction.

    Setting Conditions:
    Key on or engine running, and the AF ECU detected an unexpected voltage condition on the Natural Gas Output Enable, High Pressure Lockout, Low Pressure Lockout or MIL control circuit for 1 second.
    This code sets in 1 Trip(s).

    Possible Causes
    Natural Gas Output Enable, High Pressure Lockout, Low Pressure Lockout or MIL control circuit is open, shorted to ground or shorted to power.

    Alternative Fuels ECU is damaged or has failed

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    • #3
      Re: CNG not working, DTC P1215?

      If you have any reason to believe the AF ECU is damaged, you should go to E-bay. There is one listed--these are no longer available (there might be one left at GM for about half the value of the car ). I would suggest you pick up the E-bay item.

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      • #4
        Re: CNG not working, DTC P1215?

        In addition to the lock out solenoid coil, there is a diode in parallel with the coil to prevent a voltage surge when the AF ECU opens the ground connection to close the low pressure lockout valve. You should make sure this diode is not shorted and part of your problem. Is the AF ECU working at all which would be indicated by a red light coming on on the fuel gauge selector switch for a moment and then going out when you first turn on the key? I would assume the 20 amp CNG fuse is OK as it is the AF ECU that sets the DTC you are getting. For a test, you could take the connector off that goes to the low pressure lockout valve and put a test lamp across the terminals. When you turn on the key, the red light on the fuel selector switch should come on for a second and then go off. You should also hear the high pressure lockoff valve in the trunk open for a second and then close. The light on the low pressure lockoff connector should not light. When you start to crank the engine, the light should come on. If you don't hear the lockoff valve in the trunk open or you have no light, the AF ECU is most likely bad. If you can wrangle the one on E-bay you should be just fine.

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        • #5
          Re: CNG not working, DTC P1215?

          Originally posted by siai47 View Post
          If you don't hear the lockoff valve in the trunk open or you have no light, the AF ECU is most likely bad. If you can wrangle the one on E-bay you should be just fine.
          Well, before I had the low pressure solenoid replaced, I could hear the valve in the trunk open. Now it doesn't. So I would want to know 100% what's causing the problem before buying anything else, which probably means a trip to the dealer. And if I do have to replace the AF ECU, I'll probably have to pay the dealer to re-flash it; what's a reasonable price to pay for that?

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          • #6
            Re: CNG not working, DTC P1215?

            If you have to replace the AF ECU from the dealer (providing the dealer can get one) you will be looking at more money then can be justified based on the value of the car. I would think you would be looking at close to $2000 for the repair--The dealers cost on the ECU is around $1400 plus labor to install and flash. A quick trip to the dealer to confirm the problem is in order. He will give you an estimate and you can make your decision. Again, if your ECU is bad, your only option might be a used ECU and as I said before, there is one on E-bay. It is from a 2002 and might work with the current programming. I am not sure the AF ECU can be re-flashed--some ECU's can, others can not .

            I know this is difficult to think about but before spending a lot of money for this repair, you might want to consider scrapping the car. Removing the fuel filler, fuel tank and bracket, HPR, fuel lines, AF engine components, etc. still leaves you with a running car. A junk yard could provide air cleaner and trunk liner parts necessary to make the car look like a regular car that could then be sold. Selling the car and the CNG components would most likely net you enough money to buy a functional Bi-fuel Cavalier at todays market prices. You might even make a profit on the deal .

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            • #7
              Re: CNG not working, DTC P1215?

              Where is this diode? Before the solenoid was replaced, the fuel light would go off, then back on again when starting. Now after replacing, it doesn't.

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              • #8
                Re: CNG not working, DTC P1215?

                Here is a wiring diagram for the circuit
                Attached Files

                Comment


                • #9
                  Re: CNG not working, DTC P1215?

                  I have my first CNG ride this month. 02 cavalier that has a problem very similar to yours in description. Initially did not start on CNG unless car was warmed up. I notice that the instrument panel did a shutter when the ignition was turned on as it cycled the fuel indicator light on then off. Now there is a just visible flash of the fuel indicator lamp on startup and no indication it is a bifuel vehicle at all. Just kicks on in gasoline mode with no shutter of instruments at all. I did have a slight odor of CNG when car did operate properly. I am interested in what you found on your vehicle as this could prove helpful to me. Any help out there is appreciated. I did clear three error codes yesterday when the system was working again. P1202, P0202, & P1138. All fuses are good and connections all seem secure and clean.

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                  • #10
                    Re: CNG not working, DTC P1215?

                    Your first code P1202 is CNG related for sure. P0202 relates to gasoline operation only (over or undercurrent of the #2 cylinder fuel injector) P1138 relates to the oxygen sensor and could have been set by P0202. P1202 comes from the dreaded GMS/MCV unit that is the almost square thingy located on top of the engine and connected on one end to the low pressure regulator. The GMS part senses the actual gas flow through the engine when running on CNG and compares it to the desired flow. It then sends a signal to the MCV part of the unit which operates a valve to control the amount of gas flow so that the actual and desired flow are equal. If the unit is not responding and is "out of range" (in this case below the operating range of the unit) P1202 is set. A lot of times this code is set when cranking the engine and the sensor does not respond in time for CNG operation to comence. If everything else is normal, CNG operation should resume after you start to drive. However, if the gas mass flow sensor (the part that senses the acutal flow) is defective or dirty, you might never get to CNG operation. These units are not servicable (per GM who would like to sell you a new one to help pay off their government loan) but some people have been able to clean them (Lancer Automotive on this forum, for example). That being said, the other problems you mention and the other codes you have might mean you should take a second look at the wiring on your car. Make sure you check all the connectors for any corrosion and correct fit. Make sure there are no harnesses chafing. Check the harness going to the GMS/MCV on the engine and the harness connecting to the AFECU. You must remove the drivers side headlight to get to the ECU and the four relays that are mounted above it. The P0202 (gasoline) problem should be really noticable as a miss and loss of power in the engine and is most likely a wiring issue. Again, double check all the connections, clear the codes and if P1202 is the only remaing code, it is time to have the GMS/MCV looked at or replaced. There have been a couple on E-Bay with a buy-it-now of $200.00. It's easy to change and it would be a good idea to have spare in stock .

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                    • #11
                      Re: CNG not working, DTC P1215?

                      My thanks to siai47 for the help on identification of trouble. This string was great for troubleshooting my issue. I found four problems and have corrected three.

                      A wire on the low pressure valve was worn through and in contact with a steel reinforcing wire of the low pressure side of the gas flow control valve assembly.

                      Lead acid battery had a leak and was dripping on wire harness connection below battery. High humidity days the brain would go dead.

                      AF ECM was terribly corroded from road salt. Aluminum oxide flake on full perimeter and connectors had oxidation inside of boots and just working into module. Cleaned up unit and connectors and have not had a dead unit since.

                      Final item not corrected is the low pressure regulator is leaking by the diaphragm causing periodic starting issues. I have not rebuilt this item yet but will as soon as I can get the parts. I am leaking an estimated 1/3-1/2 a liter of CNG/minute at atmospheric pressure when system is operating based on the size of soap bubbles rising off regulator exhaust. Stinks up the car when at idle and creates a bit of a fire risk I must eliminate. This may clear up all of the codes. Off to find that part now by correcting low pressure caused by leaking out when parked.

                      My thanks to everyone that has posted on CNGCHAT.

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