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themow
New User
Sep 29, 2012, 7:37 PM
Post #1 of 5
(1906 views)
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Civic electrical issue
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I have a 97 Civic HX with 220k on it. It recently had a full tuneup including timing belt, waterpump, egr chamber cleaning, fuel filter etc. It ran great for 3500 miles and then started acting up and idling bad. I got a code p1508 for IAC. I replaced that and nothing changed so I replaced it again still no change. Ran horrible off throttle and on minor throttle. Adjusted TPS to factory specs still no change. I replaced the ECU and the idle issue and code p1508 went away. Then I got a new code P1162 for a primary 5 wire wideband o2 sensor. So I had a hairline crack in the exhaust manifold so I figured Id replace that and the o2 which im in the process of right now. Now onto the real issue. I connect my scanXL and obdlink to the car and watch live data. My concern is my coolant temp sensor. On my scanXL the temp wildly fluctuates with the car off or running. If I unplug the sensor, it still fluctuates although a little bit differently. It occasionally ready the proper temp then goes down to 30F and up to 400F. with the car off!!. Now since it does this even with the sensor unplugged, I think i can rule out the sensor.?? I have tested continuity from the positive side of the plug to the body and dont get any. When I test the green(ground I think) side of the plug, to the negative terminal, I get about 3 ohms. I am out of ideas. Please point me in a direction. Is it possible that this issue is related to what caused my ecu to fail?
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nickwarner
Veteran
/ Moderator
Oct 1, 2012, 2:56 PM
Post #2 of 5
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Re: Civic electrical issue
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I'm in doubt that your original ECU was bad in the first place. You certainly are getting a voltage drop on the temp circuit and I would do a voltage drop and wiggle test on it.
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themow
New User
Oct 1, 2012, 5:10 PM
Post #3 of 5
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Re: Civic electrical issue
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So are you saying that the electrical issue fried the ECU? When I plug the old ecu in, the car runs horrible with a bouncy idle and bad fuel smell. I have done a wiggle test on the whole harness and can not reproduce or change the outcome.
(This post was edited by themow on Oct 1, 2012, 5:10 PM)
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nickwarner
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/ Moderator
Oct 1, 2012, 5:47 PM
Post #4 of 5
(1840 views)
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Re: Civic electrical issue
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Ok, maybe the ECU was bad. Lot of people condemn them without proper testing but seems like you have a better handle on it than most. You would need a good schematic with connector views like a factory manual or alldata has to do what I would suggest. I don't have access to that myself here. What I would do is disconnect the PCM bulkhead connector completely along with the temp sensor. Wire up a small 12v light bulb like a marker light or dome light thqat has a pigtail to have pins which you can jump into the plug for the temp sensor. Now place jumpers on the PCM plug to the power and ground of that exact circuit. The bulb should turn on. Hook up the voltmeter (although a scope with video capability would be much better to find glitches) in a voltage drop test. Do your wiggle test. Repeat on the ground side of the circuit. See what readings you get. The little light bulb may dim as well, showing visually the voltage drop like the sensore is getting. Very important not to just backprobe the connector with the PCM connected or damage will be done.
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themow
New User
Oct 3, 2012, 6:50 PM
Post #5 of 5
(1820 views)
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Re: Civic electrical issue
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Im not exactly sure I understand your testing method. I have the factory service manual so I can find what ecu connector is what. Youre saying to pull the ecu and coolant sensor plug. Wire a light into the plug and apply 12v to the ecu coolant temp wires? It should read a steady 12v. Is this correct?
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