AEM Series 2 Coolant Temp Issue

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ChasingSand

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I got a weird situation happening and was hoping maybe someone has experienced this or dealt with this before.

When I had my car tuned, the tuner told me the coolant temp sensor was not working. He was able to bypass this and still tune the car.

Fast forward, I replaced the sensor and now the car is still having showing a coolant temp fault. 

Here is where it gets weird, if I plug in my OEM ECU it reads just fine, showing ambient temp and will raise or lower as needed.

I have tested 3 different sensors and they all have the same fault. I sent the ECU to AEM and they replaced a burnt resistor and said everything is functional. Plugged it in today after the repair and same issue. 

The doubt there is an issue with the Harness as it works fine with the Stock ECU, but am not 100% sure.

The sensor is putting out 5.10 volts cold and slowly rises as the temp warms up, but the car dies around the 170 degree mark as bumps up the injector pulse and floods the motor.

I called AEM and they are stumped as well. 

Any Thoughts?

 
Did the tuner do anything within the tune that needs to be undone now that you have a working sensor?

 
LtPyro said:
Did the tuner do anything within the tune that needs to be undone now that you have a working sensor?
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I thought that might have been the case, so I removed the tune and uploaded the AEM base tune and it threw the same error.

They had me plug the Intake air temp plug into the coolant sensor to see if it created an error and it did not, so its really pointing to a fault in the ECU.

After speaking with AEM they want me to send it back to them to revaluate. 

Kind of stuck with that option as I dont want to drop 1500 on another ecu.

 
Carwashguru said:
I thought that might have been the case, so I removed the tune and uploaded the AEM base tune and it threw the same error.

They had me plug the Intake air temp plug into the coolant sensor to see if it created an error and it did not, so its really pointing to a fault in the ECU.

After speaking with AEM they want me to send it back to them to revaluate. 

Kind of stuck with that option as I dont want to drop 1500 on another ecu.
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Weird, well hopefully AEM figures it out or they replace it with a working one.  I bought two AEM S2 ECU's and one had a bad injector channel on it causing my dads car to hold an injector open while running.  AEM didn't catch it but the tuner did and mapped it to another injector channel.  

 
Glad you finally got your issue figured out! I was wondering what ever happened.

With that issue did you send it back to AEM for them to evaluate it?

I sent mine to them yesterday so should have an update early next week hopefully.

Very close to just buying another one at this point.

 
Are you sure you're not shorting anything to ground on that circuit?  

 
Carwashguru said:
I dont believe so as the circuit is completely fine when running with the stock ecu.
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Could just be the stock ECU can handle more current through that circuit.  Check for ground on the plug to rule it out, otherwise you'll just keep burning up AEMs.

 
I don't think you should ever read over 5 volts. Its a 5 volt reference signal going through 2 resistors (ecu has one and sensor has one). 5 volts should be when your at like -40 degrees, 0v when at like 420 degrees or something. What do you get on the harness end between the 2 pins when it is unplugged (while powered on)?

 
Travelah said:
I don't think you should ever read over 5 volts. Its a 5 volt reference signal going through 2 resistors (ecu has one and sensor has one). 5 volts should be when your at like -40 degrees, 0v when at like 420 degrees or something. What do you get on the harness end between the 2 pins when it is unplugged (while powered on)?
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When I unplugged the sensor and ECU was powered on, I would get 4.98 volts from the ECU.

I did try 3 different sensors and they all gave the same read out in the AEM software (5.08 Volts)

 
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I would suggest sending one of those sensors to AEM When you send them the ECM.

 
Carwashguru said:
When I unplugged the sensor and ECU was powered on, I would get 4.98 volts from the ECU.

I did try 3 different sensors and they all gave the same read out in the AEM software (5.08 Volts)
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Any voltage on the return wire if it's unplugged from the sensor?

 
Carwashguru said:
How would I test that?
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Set to VDC, red probe on the return voltage pin, black on known good ground.  If 0, good.  If 5.x volts like above, something is putting voltage into the circuit.  Could be the ECU, could be the harness.  Hard to check, but likely culprit could be the 5.0V feed to the sensor, so check continuity across the pins on the coolant sensor connector.

 
That is frustrating...  but if they own up to it and getter done...  👍👍👍

 
Even though they messed up, glad to hear they caught it, owned it and are getting it fixed

 
Carwashguru said:
Just got off the phone with AEM. Turns out the first repair was not completed correctly! 

Not sure how that happens but should have the ECU back in the car in a couple of days and will report back.
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Did they go into detail at all?

 
This is what they stated in their email today:

Verified unit had coolant issues. Found the EMS to have a burned 5 volt reference and sensor ground circuit. Repaired damaged circuit and found all sensors to be fully functional. Fully tested all hardware functionality and found all Injectors, Coils, Sensors, High sides, Low sides, IDLES, Analogs, PWS, Cam and Crank, VSS, Relay circuits, and Voltage regulators to be fully functional.

 
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