P2121 DTC after Auto Conversion

The accelerator pedal position sensor is mounted on the accelerator pedal bracket. The accelerator pedal

position sensor has 2 sensor elements and 2 signal outputs: VPA and VPA2. VPA is used to detect the

actual accelerator pedal angle (used for engine control) and VPA2 is used to detect malfunctions in VPA.

When the difference between the voltage outputs of VPA and VPA2 deviates from the standard, the ECM

determines that the accelerator pedal position sensor is a malfunctioning. The ECM turns on the MIL and

the DTC is set.

This error can be caused by an issue or a fault with any or all of the following:

• OEM Accelerator Position Sensor Assembly
• Aftermarket Cruise Control System that wires or connects in-line to the OEM Accelerator Position Sensor
• Aftermarket throttle controller that wires or connects in-line to the OEM Accelerator Position Sensor

First, remove all aftermarket accessories that are wired or connected in-line with the OEM Accelerator Position Sensor and drive for at least a week or until the error returns. If the error returns with all aftermarket accessories disconnected, then it is likely to be an issue with the OEM Accelerator Position Sensor Assembly.

If no error detected for a week, connect only one aftermarket accessory at a time ie: Only connect cruise control but not the throttle controller. Drive for a further week to see if the error is detected again. Test each aftermarket accessory for week individually. Then test again with combined accessories until you can isolate which product causes the errors when plugged in and doesn't cause errors when unplugged.