P0138 Diagnostic Help for 2008 Dodge Ram 1500 5.7L with Aftermarket Headers and Custom Tune
Hello, I recently installed a camshaft and long tube headers on my 2008 Dodge Ram 1500 5.7L, along with a custom tune by Jay Greene. A few weeks after the installation, the check engine light came on. To troubleshoot, I have performed several tests: - Swapped the rear oxygen (O2) sensors between banks - Swapped the front O2 sensors between banks - Replaced and re-routed the wiring harness extensions (Dynatech brand) I measured the voltage of Bank 1 Sensor 2: 1.235V, then 1.145V, and finally 0.956V — all while the truck was off and the sensor unplugged. Bank 2 Sensor 2 consistently reads 1.956V. I'm unable to identify the root cause of this issue. The only fault code present is P0138, and I have no other related codes. Could this be a wiring or sensor issue? Are aftermarket O2 sensor harnesses prone to causing signal faults? Any insights into how to properly diagnose or resolve this would be greatly appreciated.
Make sure all connections are fully reconnected. Use a scan tool to retrieve and share the full list of diagnostic trouble codes (DTCs). Confirm whether only P0138 is present — if so, note the freeze frame data. While operating the truck, check the O2 sensor B2S2 voltage via scanner. Additional considerations: - Oxygen sensors should typically be OEM Dodge or NTK brands. - Please specify any custom programmers or tuning chips used. - A common issue is a post-catalyst O2 sensor signal shorting to its heater side, resulting in high return voltage. - Aftermarket components — especially wiring extensions — can introduce electrical faults. Double-check the Dynatech harness extensions you're using; if not original OEM parts, they may be contributing to the problem.