91Pioneer Posted March 30, 2016 Share Posted March 30, 2016 So here's the deal. I bought a 92 MJ yesterday and the guy had said that he put in a replacement PCM from the junkyard. He told me which junkyard so I know it came from an XJ but I don't know what year. Here's the issue. The vehicle that had the "good" PCM had A/C, mine does not. So now I have the following DTCs: 12: battery disconnected (last 50 start cycles) 35: cooling fan relay 33: A/C clutch relay 21: O2 sensor or circuit 14: MAP sensor 47: battery under voltage 51: O2 lean mixture. Well the guy has recently replaced the O2 sensor, I don't know with what brand. So I can't say if the O2 sensor codes are still "active" since he just did that recently. Apparently the old one had burnt wires, he discovered after he removed it. And I don't have A/C so that would explain codes 35 and 33. The 14 MAP sensor code, the truck runs fine and I know the hard vacuum line going to it is connected. If I disconnect the battery and reconnect that should reset all that right? I think I should reset and then drive and see what comes back. Perhaps the PO disconnected the battery when he put in the new O2 but he may not have. Here's what I'm thinking. I should buy a used PCM from someone here who has an MJ non-AC PCM. Sound like a plan? The check engine light is not on while driving and the cat converter is gone so the only downside to any of these issues would probably be a less efficient running engine. Link to comment Share on other sites More sharing options...
HOrnbrod Posted March 30, 2016 Share Posted March 30, 2016 First thing: What's the p/n of the ECU? It should be 5601xxxx. ECU's don't care if it has A/C or not. They care about engine, transmission, and the country it's in. Oddly enough, Canada has their own ECU p/n's, just as Europe and the US do based on their respective emission regulations. It's best if we can ID what ECU you have now before doing anything else. Link to comment Share on other sites More sharing options...
terrawombat Posted March 31, 2016 Share Posted March 31, 2016 My 91-93 parts book has all ECU (technically called PCM by Chryco) P/Ns as 5602xxxx. Like Don said, no such thing as an A/C or non A/C ECU/PCM. Link to comment Share on other sites More sharing options...
91Pioneer Posted March 31, 2016 Author Share Posted March 31, 2016 56027396 date code 03/07/92. The other code under the barcode is QTQZ0301D1. Link to comment Share on other sites More sharing options...
terrawombat Posted March 31, 2016 Share Posted March 31, 2016 My parts book shows that number as an ECU for a 1992 6-cylinder engine with manual transmission. Link to comment Share on other sites More sharing options...
HOrnbrod Posted March 31, 2016 Share Posted March 31, 2016 My parts book shows that number as an ECU for a 1992 6-cylinder engine with manual transmission. Si. 1992, w/o RFI 6-Cyl. Eng., Man. Trans. 5602 7396 1 XJMJX1 Link to comment Share on other sites More sharing options...
91Pioneer Posted March 31, 2016 Author Share Posted March 31, 2016 So the ECU is correct, good. What is w/o RFI (what is RFI)? Is that the chip in the key? Is the ECU the same for both XJ and MJ? I have the truck in the garage tonight while I work on it, so I'll just disconnect the battery for an hour and then reconnect and check for codes after a few days. Link to comment Share on other sites More sharing options...
HOrnbrod Posted March 31, 2016 Share Posted March 31, 2016 So the ECU is correct, good. What is w/o RFI (what is RFI)? Is that the chip in the key? RFI is radio noise suppression Is the ECU the same for both XJ and MJ? Yes Clear the codes doing the below and start from scratch with the ECU: Clearing error codes and removing residual memory 1. Disconnect the POSITIVE battery terminal and touch it to ground for 30 seconds. (This is to discharge the PCM capacitors, which maintain the Adaptive Memory. 2. Reconnect the Battery Cable 3. Turn Ignition Switch to the "ON" position but DO NOT start the engine 4. Turn Headlight "ON" 5. Turn Headlights "OFF" 6. Turn Ignition Key "OFF" The PCM Adaptive memory has now been flashed, or erased from the PCM. Link to comment Share on other sites More sharing options...
gogmorgo Posted March 31, 2016 Share Posted March 31, 2016 Seems like every time you post that it gets more complex... What do the lights have to do with it? Link to comment Share on other sites More sharing options...
HOrnbrod Posted March 31, 2016 Share Posted March 31, 2016 I do it just to confuse you Gog. :rotfl2: Found the procedure on the interweb, and cleared it with Hesco years ago. It puts a load on the ECU and dumps all the adaptive memory. It remains if you just let it sit overnight or whatever with the battery disconnected. It does work. Try it yourself. Link to comment Share on other sites More sharing options...
91Pioneer Posted March 31, 2016 Author Share Posted March 31, 2016 Thanks it's too late now but I'll try that tomorrow. Link to comment Share on other sites More sharing options...
91Pioneer Posted April 2, 2016 Author Share Posted April 2, 2016 OK time for an update. Since I posted last I put my battery tender on the battery to top it up and I reset the codes using that different procedure, I didn't notice any drivability changes but I re-read the codes tonight and now I have left: 12: battery disconnected (last 50 start cycles) 35: cooling fan relay 33: A/C clutch relay 55: end of codes Well yeah those two relays are missing, they aren't required, I don't have the extra electric cooling fan or A/C. So I *think* I'm good to go now. I'm actually wondering if I should just put relays in those two spots to make the codes away or forget it and move on.... hmmm.... thoughts? Link to comment Share on other sites More sharing options...
Minuit Posted April 2, 2016 Share Posted April 2, 2016 I wouldn't worry about it. That's more or less the OBD1 way of saying "all clear" for no A/C. Certainly wouldn't hurt to check the codes every once in a while though. The OBD1 system very very rarely turns the CEL on in my experience, and I doubt it would turn it on for 33 or 35 (unless of course it's on in your truck :dunno: ). IIRC those codes are normally present on a non-AC vehicle anyway. Link to comment Share on other sites More sharing options...
HOrnbrod Posted April 2, 2016 Share Posted April 2, 2016 ......forget it and move on. Yes. But continue to monitor for these should they appear again: 21: O2 sensor or circuit 14: MAP sensor 47: battery under voltage 51: O2 lean mixture. Link to comment Share on other sites More sharing options...
91Pioneer Posted April 2, 2016 Author Share Posted April 2, 2016 How long are codes stored in memory? I think the O2 codes will be gone for good now. Link to comment Share on other sites More sharing options...
HOrnbrod Posted April 2, 2016 Share Posted April 2, 2016 You have dumped all codes from memory (except the A/C stuff since you don't have it) by doing the hard reset and are starting from scratch on the ECU factory settings. If any of the other previous should reappear, it's most likely a legitimate code and should be investigated. Time frame varies in my experience, but if nothing appears in the next 500 miles you should be good as far as the ECU is concerned. Link to comment Share on other sites More sharing options...
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