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View Full Version : Low voltage to ECU



T-spoon
02-23-2012, 04:15 PM
How should I go about tracking down a low voltage issue? Even when battery is reading 12.6 volts, my ECU (it's an AEM series 2) is only seeing 10.5 volts or so. Is this more likely an issue with the wiring through the main relay to the ecu, or the positive battery cable and it's connections? I've recently beefed up my main engine/battery grounds.

METDeath
02-23-2012, 06:07 PM
Are you testing using the same ground as the ECU or just anywhere?

Luni
02-23-2012, 07:08 PM
Measure the resistance from the connection point of the ECU to that points termination to the battery.

T-spoon
02-23-2012, 08:16 PM
Met - The voltage readout for the ECU is in the ECU itself (laptop is plugged into the AEM ecu and has all sorts of diag. readouts).

Luni - The Ecu +B comes from a body harness plug which comes from the master relay in the kick panel. I'm not really sure what wire carries the power to that relay (i have to assume it goes through the ignition switch circuit, will take a look at the EWD).. I guess I should start by getting resistance between ecu and body harness plug, then from the harness plug, to master relay, then master relay to battery?

It occurs to me just typing that (it made me actually think.. damn..), my turbo timer has not worked since the car was vandalized, but it's still plugged in.. maybe I should start by removing that jumper harness from the ignition switch.. Then again, on second thought, all the ignition circuit does is tell the relay to switch on and provide battery power.. meh, need to check that EWD

Luni
02-24-2012, 06:49 AM
Met - The voltage readout for the ECU is in the ECU itself (laptop is plugged into the AEM ecu and has all sorts of diag. readouts).

Luni - The Ecu +B comes from a body harness plug which comes from the master relay in the kick panel. I'm not really sure what wire carries the power to that relay (i have to assume it goes through the ignition switch circuit, will take a look at the EWD).. I guess I should start by getting resistance between ecu and body harness plug, then from the harness plug, to master relay, then master relay to battery?

It occurs to me just typing that (it made me actually think.. damn..), my turbo timer has not worked since the car was vandalized, but it's still plugged in.. maybe I should start by removing that jumper harness from the ignition switch.. Then again, on second thought, all the ignition circuit does is tell the relay to switch on and provide battery power.. meh, need to check that EWD


Yep Spoony, thats the way to do it.

kado1000
03-15-2012, 03:14 PM
my car does the same thing