dgsav Posted July 15, 2012 Share Posted July 15, 2012 (Long time lurker, long time borrower of other members' knowledge, newbie poster of own problems) I have an '88 GL wagon 5 speed dual range 4WD with 260K miles that's been in my family since new (I actually drove it off the dealer lot with 10 miles on it). Car is essentially stock and has been mechanically well maintained. Replaced engine at 213K, probably unnecessarily, and it's been running well all along. Last week the Check Engine light started coming on intermittently. I checked the ECU LED and found stored codes 23, 24, 34. I diagnosed the MAF sensor (23), the IAC (24), and EGR solenoid (34) per the FSM and they all checked out fine. The FSM flow charts conclude that the ECU has failed. I don't think I believe that, unless the alternator voltage regulator failure (overvoltage) 18 months ago has just now become an issue. I cleared the codes (actually, I removed the ECU and visually inspected it; looked fine as I had expected). A short test drive brought back the intermittent CEL, mostly toward the end of the drive, and a stored Code 34. I gather from lurking that EGR solenoid failures are not uncommon, although mine electrically checks out. Also, I know EGR failure does not affect performance, so the car would run fine. My car starts and drives just like it has done for 23 years, but the CEL is new and annoying. Aside from fuel pump driver issues, has there been experience with these ECUs starting to fail as they age? I've always thought that if an electronic unit didn't fail right away, it pretty much wouldn't fail at all (assuming no electrical or environmental mishaps). I'll continue to test and monitor the car, but I welcome any thoughts. Quote Link to comment Share on other sites More sharing options...
GeneralDisorder Posted July 15, 2012 Share Posted July 15, 2012 Electronics can fail from age. Especially capacitors like to start leaking and transistors will occasionally burn out from heat cycling. But I would guess that you are fighting a resistance battle with your grounds or power supplies. Checking the voltage and the resistance per the FSM is not sufficient to tell you if the wiring will carry a 10 amp draw without voltage drop. You really need to perform a voltage drop test with a load in the circuit that approximates the load of the EGR solenoid. You may have a corroded ground connection or a bad connection at your fusible link that supplies power to the ECU.... for example. These come in handy for what you are about to test: http://www.esitest.com/180.html GD Quote Link to comment Share on other sites More sharing options...
FlatFourFrenchy Posted July 16, 2012 Share Posted July 16, 2012 If yours codes are all over the place I would start with checking all your grounds. I once had a 93 VW Eurovan. Started bucking on highway if I tried to keep it at any steady speed. After many attempts to isolate cause, I found that the chassis negative wire from battery was loose. My ecu was trying to find ground through the drive axles to the engine ground (-). It can make for a very simple and free fix if that is it. Good luck Quote Link to comment Share on other sites More sharing options...
Gloyale Posted July 16, 2012 Share Posted July 16, 2012 Last week the Check Engine light started coming on intermittently. I checked the ECU LED and found stored codes 23, 24, 34. I diagnosed the MAF sensor (23), the IAC (24), and EGR solenoid (34) per the FSM and they all checked out fine. The FSM flow charts conclude that the ECU has failed. I don't think I believe that, unless the alternator voltage regulator failure (overvoltage) 18 months ago has just now become an issue. Did you test continuity on the wiring end to end, from ECU to MAF? I had these excact 3 codes in a car last week. MAF and IAC codes were both from broken wiring. I had to run a new wire to the ECU for MAF, and replaced one wire to the IAC. Quote Link to comment Share on other sites More sharing options...
dgsav Posted July 20, 2012 Author Share Posted July 20, 2012 After clearing the ECU, Codes 23 and 24 have not returned. I now suspect they may have been stored for many months from past episodes of fiddling with the connectors and setting minimum idle speed. The ECU memory evidently does not clear itself if a problem doesn't come back after several engine restarts. All the wiring is in excellent condition, as are all grounds. While Codes 23 and 24 have not come back, Code 34 has, along with the intermittent CEL. I've traced it to the EGR purge solenoid having excessive resistance (several K ohm) when it gets hot. I suspect the solenoid winding is going open circuit when the engine warms up. Since I have to meet biannual smog inspections, replacing the solenoid with a 33 ohm resistor is unfortunately not an option for me. I'll pursue replacing the solenoid. Thanks for all the ideas, everyone. Quote Link to comment Share on other sites More sharing options...
WoodsWagon Posted July 21, 2012 Share Posted July 21, 2012 I used a solenoid out of an 80's cadillac Seville for mine. Evap solenoids are really common, just make sure the resistance is in the right range and splice it in. Don't limit yourself to subarus at the junkyard when looking for a replacement. Quote Link to comment Share on other sites More sharing options...
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