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Forum namePerformance/Engine
Topic subjectNo power to ECU, car won't start. Please help!
Topic URLhttp://forums.2gnt.com/dcboard.php?az=show_topic&forum=5&topic_id=138055
138055, No power to ECU, car won't start. Please help!
Posted by JasonST, Dec-31-69 06:00 PM
I own a 95 GS and it's worked fine until 1 day I go to start it and it would crank and crank but not start. I quickly realized the check engine light wasn't coming on, and the fuel pump and ASD relays weren't clicking.
I did as much diagnosing as I could but could really use some help. I've checked all the fuses especially the 30 amp engine fuse and all are good. I get 12V to 2 pins on the ASD relay so that looks goods. Only things I can find is that the black/red wire going into the ECU at pin 2 has no power going to it and I think it's suppose to be main power for the ECU according to this http://www.2gnt.com/index.php?d=1995_ECU

.... So I checked for reference voltage to all the sensors and everyone is below 1 volt but higher than half a volt with the key on. Any help would be appreciated.
138056, RE: No power to ECU, car won't start. Please help!
Posted by DirtMegirt, Dec-31-69 06:00 PM
I had an issue where my 95 wouldn't start and, like yours, the check engine light wouldn't light at all. Swapped out the ecu for a known good one, all taken care of. Do you have another ecu to swap in? I believe i read that 95 ecu's are prone to failure. I started carrying a back-up in my car incase i get stranded somewhere. Hope this helps.
138063, RE: No power to ECU, car won't start. Please help!
Posted by JasonST, Dec-31-69 06:00 PM
Hmm, I'll replace the ECU as a last resort. They seam to go for a couple hundred dollars online.
Does anyone know why the ASD relay, the fuel relay, and the ECU all would lose power? Not just 1 but all 3? I wish I had a wiring diagram. Thanks.
138065, RE: No power to ECU, car won't start. Please help!
Posted by Wes Tank, Dec-31-69 06:00 PM
The ignition switch triggers the asd relay which triggers the ecu which triggers the fp relay if I remember correctly. ECU could be burnt out. It's especially common with the 95s.
138068, RE: No power to ECU, car won't start. Please help!
Posted by valdeelrico, Dec-31-69 06:00 PM
Get a multimeter and check for voltage and continuity. Continuity is checking a bus or wire for 0.0 resistance.

Unplug the wire harness for the ECU and check for voltage with the key tuned to "ON". Find the pin that has power coming into the ECU and see if it reads 12v check from this pin to ground, NOT the ground pin but chassis ground (from the power pin to a bolt on the frame).

If it does not read 12v check your battery to see what the voltage is across the battery terminals. What every is at the battery should be the same from the pin to the chassis.
If the power reads lower at the pin than it does at the battery then you have a bad wire. all the voltage cannot reach the ecu.

if all is good so far check the positive 12v pin to the ground pin. then check the ground pin to the positive battery terminal. All these readings should be the same.
Now check the ground pin to the ground chassis for continuity you should get 0.0 resistance check a few different spot on the car to make sure you get 0.0 resistance. Rust oil and other thing could show resistance on the meter.

Let us know how it goes. Come back for questions and updates.
138080, RE: No power to ECU, car won't start. Please help!
Posted by JasonST, Dec-31-69 06:00 PM
Alright. So I think I FINALLY got somewhere. From what I tested it's got to be the ECU as the culprit. Here's what I did.
I tested all grounds and they tested good, I tested the 2 power wires, 1 received 12v, and the black wire with red stripe didn't. However once I jumped the ASD relay it received power. Once I did this the coil also got 12V so I know the ASD relay and wires are all good. The ECU gets power and ground going into it, but it's not sending anything back, so the ECU has gotta be toast.

Before I got and fork over $200 to Satan, can anyone think how it could be anything else but the ecu? I've got power and ground going into it, and no signals at all coming out of it. NO check engine light, the ASD relay will not come on unless jumped, and same for the fuel pump relay. Thanks for the help so far!
138108, RE: No power to ECU, car won't start. Please help!
Posted by JasonST, Dec-31-69 06:00 PM
Alright, so for future reference, it was the ECU. Forked over a couple hundred dollars for a new one and that fixed the problem. So I guess you have to jump the ASD relay before it'll send full power to the ECU, the ecu must do that on it's own. SO when diagnosing make sure you jump the relay than you should have power going into the ecu on the red/black wire. Hope this helps someone in the future.
138111, RE: No power to ECU, car won't start. Please help!
Posted by valdeelrico, Dec-31-69 06:00 PM
Sounds good. DC wiring can be a hassle to test but to identify the actual device causing the issue is just a process of elimation. Good Work and Congratulations!!!!
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