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2002 Chevrolet Cavalier (Bi-fuel) OBD II port trouble

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  • 2002 Chevrolet Cavalier (Bi-fuel) OBD II port trouble

    Been a while. 4 years ago I bought a 2002 Chevy Cavalier (Bi-Fuel) for my daughter that had about 10K miles on it (has about 45K now). It has been running rather well but recently the Check Engine light illuminated (no observable performance issues). Put the scanner on it and the scanner would not power up. Read some posts online that seemed to implicate a possible blown fuse and I checked all in cabin and under hood fuses - does not appear to be a fuse and all electronics are working (including cigarette lighter). Went online to see if I can get the schematics and I'm not having much luck. There are a few people selling the hardback factory service manuals but they are a bit pricey for a 17 year old car.(lowest $135) and I really do not want a Haynes repair manual. Guess I could buy an electronic version but I really like the information in the factory service manuals. I do not want to rewire the OBD II connector and believe this is probably a wiring issue somewhere. I've tried 2 different scanners that work fine on all my other vehicles (2-2000 Civic GXs, 2001 Civic EX, 2008 Civic GX, 2002 Chevy Express Van (Bi-fuel), 2010 Ford F-150 (IMPCO BI-Fuel conversion) so I do not believe it is the scanner(s).

    1. Anyone got the schematics (connector to source) for the OBD II port that covers a 2002 Chevy Cavalier & possibly Bi-Fuel supplement?
    2. Anyone else having a similar issue with using a scanner on this car?
    3. Anyone got the factory repair manuals for a reasonable price?


  • #2
    Joe , this might sound crazy but I think some of the cng non fuel injected bi fuels were OBD I Is this the year with just 1 ecm, but injectors on the gasoline side only ? I might be wrong on this one.


    • #3
      Might try a pm to siai47, the resident Cavalier Guru.


      • #4
        Thanks for the suggestions Lakewoo90712. I was hoping he would see it but if he is like me, he probably does not frequent this forum as much these days. I thought everything in the US after 1996 was required to be OBD II compliant for emission purposes. The connector in the vehicle is the ODD II style connector. I'm thinking it is a wiring problem for power (Pin 16 does not have power). I need to trace it back and the weather here has not been cooperative (cold/snow/ice). I guess I can't fully blame the weather since I could move it to the heated garage - partly laziness on my part and I don't like to do any wiring trouble shooting without schematics. The old saying goes don't fix it if it ain't broken but there is something probably there. I don't use this vehicle (daughter's car) but I did notice that when I moved it to clear some snow the other day the light was off but I think it was running on gasoline instead of CNG so the check engine light might be an output of the CNG ECU. I believe below a certain temperature the car will start on gasoline although it has CNG. Hope I don't need that GM Tech II scanner for this car, got several nice ones but not all have all vehicle specific parameter definition. Had a problem with a 1999 in the past and had to take it to a shop and found out the CNG ECM was bad - took a while to get a good used working replacement. It does run on CNG so the CNG ECM is probably working. Unfortunately any significant CNG system problem will probably result in me disabling the CNG system since gasoline is about the same price as CNG around here (Overland Park, Kansas). Good to hear from you.


        • #5
          I don't have my Cavalier manuals down here in Florida, however the power to the OBD II connector relies on power through the same circuit that powers the lighter. A trip to a "friendly" Chevrolet dealer should be able to produce a page showing the section of the wiring harness that provides the power to the OBD connector. Unfortunately you will need a Tech2 to diagnose a problem with the car if it is related to the CNG system. No other manufacturer of scan tools bother to include the PID's (the instructions to the scan tool to read values related to specific codes) for the CNG system. For most scan tools, the CNG system in a Cavalier is invisible to them. That being said, the Tech2 also provides an external power connection to the scan tool for situations where there is no power to the OBD port. It also allows you to run specific tests relative to the CNG system operation. Many independent repair shops own Tech2's to service pre 2014 GM vehicles as they have become inexpensive to purchase now the GM doesn't support it any longer. The most basic thing that will set the MIL (malfunction indicator lamp) to on in Cavalier is the ability of the AF-ECU (Alternative fuel engine control unit) to send a code to the gasoline ECU that the AF-ECU is not ready to operate. Your 2002 Cavalier is the first year that does away with the AF-ECU and incorporates those functions into the normal gasoline ECU (ECM). A failure in any CNG component that talks to the ECU will also send a MIL request until it is resolved. You don't need to buy the complete Cavalier service manual set to service the CNG system. In fact most sets don't even have the CNG supplement (which is what you need). It shows you how to diagnose the CNG related DTC's and includes a flow chart on how to test for problems. They are out there for a lot less then the entire hard copy sets. Armed with the supplement and a Tech 2, is the only way to find out what is going on. Because of lack of power to the OBD connector, if you want to shoot from the hip without any diagnostic aids, try looking at every electrical connector (engine and body related) on the car. Take them apart and check for displaced pins or corrosion. Spray a little WD-40 on the pins and put the connectors back together. This includes the ECM connectors. Also check and clean all the grounds going to the engine where the transmission mounts to the engine. Best of luck to you. BTW--I am extremely surprised that you found a scan tool (other than a Tech2) that read any of the CNG related codes on a 2002 express van. If you had one that did, it should work on the Cavalier. The 2002 Express used the AF-ECU design like the pre 2002 Cavaliers and used a similar PID table to operate.


          • #6
            siai47 - Thank for the input. I have several bluetooth scanners (ELM 327 chip) and a Foxwell NT630. Had a couple others (ELM 327 Bluetooth) but gave them away since I was not using them much. I did not realize the 2002 Cavalier did not have a CNG specific ECM (I remember the CNG ECM that mounted behind the drivers headlight in the 1999 bi-fuel Cavalier). I gave the 1999 service manuals (including CNG supplement) to the guy who bought the 1999 Cavalier years ago. Never thought I'd buy a CNG cavalier again but ran into one with really low miles at an auction. If you are saying that there is only one ECM then this check engine light must not be on all the time from some non-existent AF ECM since it was not on when I moved the car the other day. My daughter is not as observant as me on this stuff so I'm probably not getting the full story. You bring up a good point on the Tech 2 having external power. I think the Foxwell NT630 will power from the PC/USB connector - might try using a USB cigarette lighter adapter for power and see if it works. If what you say is true I may only see the standard OBD 2 parameters.. I can't remember if I ever had CNG related codes on the Chevy Express but it did read codes associated with misfires (ended up being a distributor issue). I may look for a used Tech 2 but I'm not interested in spending a lot of money. That is why I paid a non-GM shop with a Tech 2 to help diagnose the AF ECM issue on the 1999 Cavalier - They were pretty reasonable. As of the last start, the check engine light was not on and I attributed that to it not operating on CNG but that may be my misunderstanding based on the earlier Cavalier's behavior. Either way, I'd like to look at the codes to see if there is some intermittent issue. Also want to get the OBD 2 port power fixed. Thanks for the tips.


            • #7
              Update (2002 bi-fuel Cavalier with OBD2 communication issues) - So I powered the scanner (Foxwell NT630) from a cigarette lighter adapter (USB) and the scanner came alive but would not communicate. Tried communicating to the PCM and BCM - no luck. Not sure whether the OBD2 port wiring is messed up or there is some fundamental problem with the control modules. I saw some YouTube videos that were showing OBD2 issues on 2002 Chevrolet vehicles (no power & no communication) when certain sensors were failed. Seemed weird but they were showing a scanner (Actron) that was not powering up and when they unplug the problematic sensor the scanner came alive and they were able to communicate. Interesting thing is that the MIL is not illuminated and the car is not having any issues that I know about. The reason I was looking at this again was that I was hoping to get access to the BCM to program another key FOB. My daughter lost one and there is only one that works with the vehicle - I bought two replacement key FOBs thinking programming would be an easy task not knowing at the time it requires a scanner to add a key FOB. Guess I'll need to buy a set of factory manuals and troubleshoot further. I thought this would be a simple task and it is turning out to be way more complicated.