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Aftermarket Exhaust Causes P0155 O2 Sensor Code on 2004 Chevrolet 2500 HD

Model: Unknown Fault Code: P0155 Posted: 2014-07-06 18:11

I recently installed a DynoMax aftermarket cat-back exhaust system on my 2004 Chevrolet 2500 HD truck. Since the installation, the vehicle has started triggering a P0155 diagnostic trouble code. I've observed that under normal driving conditions and especially when towing, the check engine light does not illuminate—meaning the code appears only under certain conditions. I have cleared the code multiple times, but it consistently returns. Is there any solution other than replacing the Bank 2 O2 sensor? The exhaust system is a cat-back design installed entirely downstream of the existing oxygen sensors, and no wiring splices were performed on the sensor harnesses.

Related fault codes
P0155
Comments (6)
Anonymous 2014-07-06 19:42

Did you need to splice or relocate any existing O2 sensor wiring during installation? If so, a change in heater resistance could trigger the P0155 code due to improper sensor heating circuit operation.

Anonymous 2014-07-06 20:57

No, I did not modify or splice any of the original O2 sensor wiring. The DynoMax exhaust is a cat-back system installed entirely downstream of both O2 sensors, so no interference with sensor harnesses occurred.

Anonymous 2014-07-06 22:44

Given that no wiring modifications were made, it's unlikely the issue stems from a physical connection. The P0155 code specifically indicates Bank 2 Sensor 1 is not reaching operating temperature and points to heater circuit or resistance problems as the probable cause. Before replacing the O2 sensor, consider measuring its heater resistance for normal operation.

Anonymous 2014-07-07 06:50

Could it be safe to assume that Bank 2 O2 sensor failure is the root cause? The timing of the P0155 code appearing after installing a new exhaust seems coincidental, but I'm not sure if there's any direct link between the two events.

Anonymous 2014-07-07 08:23

Measure the heater resistance between the O2 sensor ignition feed and ground at the sensor pigtail. The acceptable range is typically 3.5 to 14.0 ohms. This test can help determine if the heater circuit is functioning properly. All other components—including the original AC Delco sensors—are stock and unmodified, except for the aftermarket exhaust.

Anonymous 2014-07-07 09:32

I'll perform the resistance check at the pigtail as suggested. The rest of the system remains stock with original AC Delco O2 sensors, and only the cat-back exhaust has been changed.