2002 Chevy S-10 Repeated P0155 Code: Diagnosis and Fixes

Is your engine a 2.2L or 4.3L variant?

It's a 4.3L engine.

The P0155 code refers to the Bank 2 Sensor 1 oxygen sensor heater circuit. This is a ground-side circuit, controlled by the Powertrain Control Module (PCM). Pre-cat O2 sensor heater circuits are powered side-switched and rely on a constant ground from the PCM. To properly diagnose this issue, you’ll need a scan tool with bi-directional controls to command the heater circuit on/off — allowing the PCM to pulse power in a controlled manner for testing. A scope is recommended to monitor the pulse width modulation. The PCM provides a constant ground that can be tested using a test light connected between battery positive and the sensor connector. Additionally, check the resistance of the high-control wire from the PCM to the O2 sensor. If there’s an issue on the control side, you should also see a P0135 code due to shared PCM control over both pre-cat heater circuits. Ensure that you replaced the correct sensor — Bank 2 Sensor 1. Why were you only testing the post-catalyst O2 sensor fuse? A problem in the power distribution box could result in a rear catalytic converter heater circuit fault. Please let me know if further clarification or troubleshooting steps are needed.

You can also test the resistance of the oxygen sensor heater element for proper function.

Thanks for the detailed explanation. I don’t have much electrical knowledge and only have a basic code reader and test light. I swapped the upstream O2 sensors side-to-side — the P0155 code changed to P0135 and P0154. When I swapped them back, placing the original Bank 2 Sensor 1 into its position, the P0155 code returned. This suggests that the sensor itself may not be the root cause. I replaced the original sensor with a Bosch O2 sensor — still got the P0155 code. Then I swapped Bank 1’s sensor 1 with the original Bank 2 sensor 1, which triggered both P0135 and P0154 codes. After returning the original to Bank 1 and installing a new Denso sensor in Bank 2, only the P0155 code remained. I tested continuity on the signal wires from the control module to the sensor plug — all readings were good. I borrowed a multimeter for this test. Could a faulty coolant temperature sensor be contributing to this issue?

I don’t believe it’s the coolant temperature sensor (CTS). If you have access to a DC voltmeter, check the signal wires from the O2 sensors for proper voltage readings.

I tried a Bosch sensor first — no codes appeared. Then I switched back to the original Denso sensor. While it’s possible there was a subtle difference in voltage characteristics, could this have triggered the P0155 code? Could the CTS be interfering with O2 sensor operation?

I had a Bosch sensor installed in Bank 2 for some time without any codes. When I swapped sensors between Bank 1 and Bank 2, did you observe both P0135 and P0154 appearing together?

Check the signal wires from the O2 sensor to ensure proper connectivity and integrity.

I replaced the original sensor with a Bosch — still got P0155. Then I swapped Bank 1’s Sensor 1 with the original Bank 2 sensor, which triggered both P0135 and P0154. After returning the original to Bank 1 and installing a new Denso in Bank 2, only P0155 remained. I tested continuity on the signal wires from the control module to the sensor plug — all readings were good. I used a multimeter for this test. Could it be a faulty coolant temperature sensor?

I don’t think it’s the coolant temperature sensor. If possible, use a DC voltmeter to check voltage on the O2 signal wires during idle and warm-up conditions.

I’ll try getting a DC voltmeter — what specific readings should I look for?

During a cold start (COOL), check the O2 sensor signal wire at the PCM for approximately 300 millivolts. This reading is typically back-probed from the sensor connector.

I’ll get a DC voltmeter soon. Here are some freeze frame data points that may help: SHRTFT1 = 8.6, LONGFT1 = 10.2, SHRTFT2 = 5.5, LONGFT2 = 11.7, ECT1 = 29°C (the truck had been off for about 20 minutes). Oxygen sensor monitoring shows 'INC' and 'Heater OK'. MAP reading is 18.0 psi. I didn’t send this earlier — hope it helps.

Freeze frame data has limited value for diagnosing P0155. You mentioned checking all O2 sensor wiring initially. The issue with no power on the post-cat O2 heater circuit fuse suggests a potential fault in the power distribution or relay. A proper diagnosis requires actual testing — such as measuring voltage and ground conditions at the sensor. Without dedicated diagnostic tools, this remains speculative. Possible causes are numerous. You may need to either perform specific tests (as outlined earlier) or visit a certified garage specializing in electrical diagnostics. With correct equipment and knowledge, diagnosing this issue should take under one hour.