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2007 Saturn Vue 3.5L: P0155 Code After O2 Sensor Replacement - Heater Circuit Open Diagnosis

Model: Saturn Vue Fault Code: P0155 Posted: 2020-02-16 12:11

I initially experienced a P0140 code indicating Bank 2 Sensor 1 O2 heater malfunction. I replaced the upstream O2 sensor, but now the vehicle is triggering a P0155 code — same sensor, heater circuit open. I tested the connector and measured 11.88 volts at the sensor terminal. The engine ground connection showed 4 ohms between engine block and battery ground. When I ran a jumper wire between engine and battery, resistance dropped to 2.5 ohms, indicating that the grounding issue is not the root cause. The vehicle is a 2007 Saturn Vue with a 3.5L engine. The O2 sensor replaced was an aftermarket unit. I plan to swap it with the Bank 1 Sensor 1 and monitor if the P0155 code moves to Bank 1 — this would suggest a wiring or sensor issue rather than a PCM fault. I also intend to inspect both upstream O2 sensor connectors for broken or grounded wires, as these are five-wire sensors. Additionally, I will use a multimeter to test resistance in the heater coil and verify voltage and current signals during lean and rich conditions using enhanced data from a scan tool. Note: Modern vehicles often have issues with aftermarket O2 sensors. The pre-cat upstream O2 sensors on this model are wide-band dual-cell sensors that require heating to approximately 1500°F to function properly. Without proper heating, they produce inaccurate signals and may trigger P0155 or similar codes. A scan tool with enhanced data is recommended for accurate monitoring of voltage and current during dynamic engine conditions.

Related fault codes

P0155

Comments (9)

Anonymous 2020-02-17 06:19

What engine size and model year? Do you have a digital multimeter (DMM) or a scan tool available for diagnostics?

Anonymous 2020-02-20 01:39

I can get a DMM. I plan to test voltage and resistance on both upstream O2 sensor connectors to check for shorted or grounded wires, as these are five-wire sensors.

Anonymous 2020-02-20 05:57

What is the exact engine size? Is it a 2007 Saturn Vue? Was the replaced O2 sensor original equipment (OE) or aftermarket?

Anonymous 2020-02-20 06:32

It's a 2007 Saturn Vue with a 3.5L engine. The replacement O2 sensor was aftermarket. I plan to swap it with Bank 1 Sensor 1 and see if the P0155 code shifts — this will help determine whether the issue is in the wiring or the sensor itself. I'll also inspect for wire shorts and compare readings between both sensors.

Anonymous 2020-02-20 11:38

Swap the O2 sensor with Bank 1 Sensor 1, clear the codes, then start the engine. If the P0155 code appears on Bank 1, it's likely a wiring or sensor issue. If not, the problem may be in the heater circuit or signal wire — possibly related to the PCM.

Anonymous 2020-02-21 02:36

Thanks for the helpful input. I'll update with my findings once I complete the testing and diagnostics.

Anonymous 2020-02-21 06:15

The front O2 sensors (upstream) are wide-band dual-cell sensors. The heater circuit receives a constant 12V feed from the PCM, which pulses ground to activate heating. Post-catalyst O2 sensors are narrow-band and use four wires.

Anonymous 2020-02-21 06:18

A DMM can be used to test the heater circuit resistance — measure the resistance of the O2 sensor heater coil to confirm proper function.

Anonymous 2020-02-22 06:28

Modern vehicles often have compatibility issues with aftermarket O2 sensors. The upstream pre-cat O2 sensors on this model are wide-band dual-cell sensors that require heating to around 1500°F to operate correctly. Without proper heating, they produce unreliable signals and may trigger P0155 or similar codes. Use a scan tool with enhanced data to monitor voltage and current during lean and rich conditions. Graphing the sensor signal under different load conditions is essential. The issue is likely either an aftermarket sensor or a wiring fault — the PCM failure rate in this case is very low.