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1999 Chevrolet K1500 O2 Sensor Codes P0134, P0154, P0155: Causes and Fixes

Model: 99 Chevy K1500 Fault Code: P0134 Posted: 2012-08-31 19:44

My 1999 Chevrolet K1500 is consistently throwing three oxygen sensor-related diagnostic codes: P0134 (Bank 1 Sensor 1), P0154 (Bank 2 Sensor 1), and P0155 (Bank 2 Sensor 1). These codes have appeared simultaneously, leading to a significant drop in fuel efficiency—from previously achieving 400 miles per gallon down to around 200 miles per tank. I'm concerned whether this could be due to a faulty Engine Control Module (ECM), but it seems highly unlikely that all three oxygen sensors would fail at the same time. Given the age of my vehicle (107,000 miles), I'm looking for reliable explanations and troubleshooting steps to resolve this issue. I've already checked the fuses and confirmed voltage supply to all O2 sensor circuits—everything reads normal. However, I'm still unsure whether the problem lies in the sensors themselves or elsewhere in the wiring harness or grounding system. Any insights or suggestions on how to diagnose and fix this would be greatly appreciated. Thanks, Bryon

Related fault codes

P0134P0154P0155

Comments (5)

Anonymous 2012-09-01 07:51

How many miles has your 1999 Chevy accumulated? A 14-year-old vehicle with over 100,000 miles is likely experiencing aging wiring or sensor degradation. The ECM is not the most probable cause—first check fuses and electrical circuits for continuity and voltage issues.

Anonymous 2012-09-02 11:15

Mohawkmtrs wrote: How many miles has your 1999 Chevy accumulated? A 14-year-old vehicle with over 100,000 miles is likely experiencing aging wiring or sensor degradation. The ECM is not the most probable cause—first check fuses and electrical circuits for continuity and voltage issues. My truck has only 107,000 miles, which makes it even more surprising that three O2 sensors are failing simultaneously. This scenario seems statistically unlikely but could point to a shared underlying issue.

Anonymous 2012-09-02 11:54

I agree—multiple O2 sensor failures at once are rare. Two of the codes (P0154 and P0155) both relate to Bank 2 Sensor 1, suggesting a possible shared wiring or heater circuit issue. Check for loose connections, corrosion, or damage in the harness connectors. Also review any recent modifications—such as off-road use in deep water—which could cause electrical shorts. A proper OBD-II scanner can help eliminate guesswork and confirm which sensors are actually malfunctioning.

Anonymous 2012-09-03 09:42

No other mechanical issues or off-roading history. Fuses test fine, and all O2 sensor circuits show consistent voltage. I'm planning to replace the oxygen sensors as a next step. While it's unusual for multiple sensors to fail simultaneously, I'll update with results after replacement and thank everyone for their helpful advice.

Anonymous 2012-09-04 18:08

Voltage readings alone aren't sufficient—verify that you're measuring full 12 volts under load. Use a test light or multimeter in a loaded circuit to ensure accurate ground and signal integrity. A poor ground connection can mimic O2 sensor faults, even if the sensors themselves are functioning properly.