Description of OBD-II DTC Trouble Code
The O2 Sensor Signals have been Swapped between Bank 1 Sensor 1 and Bank 2 Sensor 1.
What is the meaning of this?
This diagnostic trouble code (DTC) is a generic OBD-II powertrain code. It is considered generic because it applies to all makes and models of vehicles (1996-newer), although specific repair steps may vary depending on the make and model. Owners of these brands, including but not limited to Ford, Dodge, BMW, Chrysler, Mercedes Benz, Nissan, VW, etc., may experience this issue.
In simple terms, a P0040 code indicates that the vehicle’s computer (the PCM or powertrain control module) has detected that the first O2 oxygen sensors downstream from the engine have swapped wiring. The vehicle’s PCM uses the oxygen sensor readings to adjust the amount of fuel injected into the engine for optimal operation. If the PCM puts more fuel into bank 2 of the engine but detects that the bank 1 oxygen sensor is responding instead of bank 2, it triggers this code. In this DTC, the first O2 oxygen sensor located in the exhaust manifold or downstream from it is referred to as sensor #1. It is positioned upstream from the catalytic converter.
This trouble code is not common and only applies to vehicles with engines that have more than one bank of cylinders. If you have an inline engine, you will not encounter this code. Bank 1 always refers to the bank of the engine that contains cylinder #1.
Symptoms & Severity
The symptoms of a P0040 engine code may include:
This is a code that should be addressed immediately. Ignoring this code could result in damage to the catalytic converter, which can be very expensive to repair.
Causes
A P0040 DTC trouble code may be caused by one or more of the following:
Possible Solutions
A good initial step is to determine if any recent work has been done in the area of the exhaust and O2 sensors. If so, there is a high probability that the issue is caused by swapped wiring connectors for the first O2 sensor from bank 1 to bank 2.
Visually inspect all wiring and connectors leading to the first O2 sensors (located between the engine and catalytic converters). Check if the wires are intact and not burned or twisted. It is highly likely that the connectors have been swapped. If you are a DIY enthusiast, you can try swapping these front two oxygen wiring connectors as an initial repair step. Then, clear the trouble codes and road test the vehicle to see if the code reappears. If it does not, then the swapped connectors were likely the problem.
The next step would be to closely examine the O2 wiring and connectors at the PCM end. Ensure that the wires are in the correct pin locations going into the PCM and its harness (refer to a vehicle-specific repair manual for guidance). Check for swapped wires, damaged wires, etc., and repair as necessary.
If needed, perform a continuity test on each individual wire from the PCM to the O2 sensor and repair any issues found.
If you have access to an advanced scan tool, use it to monitor (graph) the O2 sensor readings and compare them to specifications. PCM failure should be considered as a last resort and may require the assistance of a qualified technician for repair or replacement.
Other related DTCs: P0041
