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Ask GM Tech (Cam) Your Own Question
GM Tech (Cam)
GM Tech (Cam), Chevy Technician
Category: Chevy
Satisfied Customers: 15181
Experience:  GM Grand Master Technician 2007. 14 years experience.
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I just replaced knock sensors and the harness and now when I

Customer Question

I just replaced knock sensors and the harness and now when I sit at idle my voltage drops down to around 12v but then picks back up to 14v within seconds most of the time. Also the check engine light has come back on with the same low voltage bank 2 code
JA: Does the light stay on, or does it blink?
Customer: Stays on
JA: What is the model/year of your Chevy?
Customer: 2001 Tahoe 5.3
JA: Are you fixing your Tahoe yourself? What have you tried so far?
Customer: Yes I replaced both sensors and the harness myself. But the same code came back. I cut the wire loom and checked the wires all the way to the fuse block and found no issues. Could this be a ecm problem. I also checked the voltage at the connector and it's only at 0.05 volts.
JA: Anything else you want the mechanic to know before I connect you?
Customer: No
Submitted: 2 months ago.
Category: Chevy
Expert:  Gary replied 2 months ago.

Hi there,

Did you torque the knock sensors to specification with a torque wrench?

Any new codes set in ECM?

Can you remove the small connector at the alternator and refit it a few times to see if this happens?

Gary

Customer: replied 2 months ago.
No new codes just the same code for lie voltage bank 2 knock sensor. My battery is now dead as well could faulty knock sensors be killing my battery
Expert:  Gary replied 2 months ago.

If it is the same code, then unlikely to be a faulty knock sensor.

A knock sensor (faulty or not) will not kill the battery.

Do you have a good battery to fit, and retest?

Customer: replied 2 months ago.
I have retested multiple times with a good battery same result. Still getting the code and still only getting 0.05 volts to the connector for the knock sensor
Expert:  Gary replied 2 months ago.

Sounds like you have an ECM fault if the harness and sensors are good.

Are prepared to swap the ECM?

Customer: replied 2 months ago.
What would be causing my voltage issue
Expert:  Gary replied 2 months ago.

I'll look up a circuit and come back to you shortly.

Customer: replied 2 months ago.
I had no voltage problems until I replaced the knock sensors and now my voltage is dropping everytime I idle and then picking back up after a few seconds and then now my battery has been completely drained .
Expert:  Gary replied 2 months ago.

Strange, I have never seen the issue you have now.

Here is the circuit for the knock sensors.

What happens to the battery/charging voltage with the knock sensors disconnected?

Are they factory sensors?

Gary

Customer: replied 2 months ago.
They are not factory or oem. And it seemed to do the same when not plugged in
Expert:  Gary replied 2 months ago.

Either you have a short within the harness, or the ECM is faulty.

One knock sensor is on C1/51, the generator field duty cycle is on C1/52.

Have you have replaced this harness all the way to the ECM connector?

Gary

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