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Chevy Yukon P0135/P0327/P0332: Knock Sensor Issues and O2 Sensor Failure Diagnosis

Model: chevy yukon Fault Code: P0135 Posted: 2015-08-18 10:11

My Chevy Yukon has recently developed multiple check engine light codes: P0135 (O2 sensor heater circuit malfunction), P0327 (front knock sensor low voltage), and P0332 (rear knock sensor low voltage). Initially, I noticed the front knock sensor was showing low voltage, so I replaced both knock sensors. After reassembly, the check engine light returned with a low voltage reading on the rear knock sensor. I then replaced the wiring harness for both knock sensors, assuming corrosion was the issue — but after reinstallation, both sensors still show low voltage (P0327 and P0332). I've now replaced both knock sensors again using generic parts (which I suspect may not be ideal), cleared the codes, and the vehicle ran smoothly for about half a day before the check engine light returned. The latest diagnostic shows P0135 active, with P0327 and P0332 pending. My questions are: Is there a connection between the knock sensor faults and the P0135 code? Should I definitely use OEM AC Delco knock sensors instead of generic ones? Are there other potential causes I should investigate? I'm at a loss here — any insights from experienced users would be greatly appreciated. Thanks in advance for your help!

Related fault codes

P0135P0327P0332

Comments (5)

Anonymous 2015-08-18 12:15

The knock sensor wiring harness is often the culprit — search online for 'Chevy Yukon knock sensor harness' to find detailed guides. Please confirm: Did you torque the sensors properly? Did you apply sealant during installation? Check for alternator AC voltage issues — a leaking diode can cause interference with knock sensor signals. If there's no knocking noise, exhaust leaks, or ticking sounds, focus on electrical circuit integrity. The P0135 code relates to the oxygen sensor heater circuit — verify fuses (especially the pink wire), ensure 12V supply, and check for proper grounding. OEM knock sensors are generally reliable; however, always inspect the wiring and circuit before replacement.

Anonymous 2015-08-18 21:10

I've already replaced the knock sensor harness. I did torque both sensors properly and applied sealant during installation. Battery voltage while running is normal, with no alternator issues. However, I recently discovered a possible exhaust manifold leak on the driver's side — though it’s not severe. The O2 sensor is reading 'open' and shows no resistance when tested — if my testing method was correct, this suggests the sensor itself may be faulty. What do you think?

Anonymous 2015-08-19 10:14

I don’t believe sealant should be applied to the sensor body — grounding occurs through the sensor housing. I’ll post more later as I’m busy today. The alternator suggestion refers to diodes — if the alternator has a faulty diode, it can produce excessive AC voltage that interferes with knock sensors. Check for this by measuring AC output from the alternator. When testing an O2 sensor, which two wires should you measure for continuity? And how do you verify grounding and 10–12V supply?

Anonymous 2015-08-20 05:49

I looked up a guide on the manufacturer’s website to learn how to test the O2 sensor — it explains checking resistance, ground connection, and voltage. I only sealed the grommet at the top of the sensor to prevent moisture from entering the engine block. I’m still unclear about how to check for alternator diode issues — could you clarify that part? Thanks for your patience and continued support through this troubleshooting process.

Anonymous 2015-08-20 09:39

Knock sensors generate an AC voltage signal sent to the PCM. In some cases, alternators with high AC 'leakage' can interfere with these signals. A simple test: Use a digital multimeter (DVOM) set to AC volts — connect it to one of the knock sensor wires while the engine is running. Tap on the engine body and observe if the voltage fluctuates. If it does, this confirms the sensor is working. For proper knock sensor testing: The resistance between the sensor wire and ground should be 93–107 kiloohms. This test helps confirm whether the sensor is functioning correctly or has failed.