Technical Description of OBD-II Trouble Code
The circuit for the throttle/pedal position sensor/switch “E” is experiencing intermittent issues.
What does that mean?
This diagnostic trouble code (DTC) is a generic powertrain code that applies to all vehicles manufactured from 1996 onwards (Dodge, Chrysler, Hyundai, Jeep, Mazda, etc.). While it is a generic code, the specific repair steps may vary depending on the make and model of the vehicle.
Based on my personal experience, a stored P2129 code indicates that the powertrain control module (PCM) has detected an intermittent malfunction in the circuit for the “E” throttle position sensor (TPS).
The TPS is typically a sensor of the potentiometer type that completes a five-volt reference circuit. It is mechanically actuated using an extension of the throttle plate shaft or a specially designed tab on the sensor. As the throttle is opened and closed, contacts in the sensor move across a circuit board, causing variations in sensor resistance. These resistance changes result in fluctuations in TPS circuit voltage. The PCM interprets these fluctuations as different degrees of throttle plate actuation.
The PCM uses input voltage signals from the TPS to calculate fuel delivery and ignition timing. It also utilizes TPS input data to monitor intake air flow, exhaust oxygen content, exhaust gas recirculation (EGR) function, and engine load percentage.
If the PCM detects a certain number of intermittent or erratic signals from the TPS over a specific period of time and under certain programmed circumstances, it will store a code P2129 and may illuminate the malfunction indicator lamp (MIL).
Severity & Symptoms
The TPS plays a crucial role in engine drivability, so it is important to address a stored code P2129 with some urgency.
Symptoms of a P2129 code may include:
Causes
Possible causes for this engine code include:
Diagnostic and Repair Procedures
A good starting point is to check for any technical service bulletins (TSB) related to your specific vehicle. There may be a known issue with a known fix provided by the manufacturer, which can save time and money during diagnosis.
For diagnosing a code P2129, I typically use a diagnostic scanner, a digital volt/ohmmeter (DVOM), and a reliable vehicle information source (ALL DATA DIY).
A successful diagnosis usually begins with a visual inspection of all system-related wiring and connectors. I also recommend testing the throttle plate for signs of carbon buildup or damage. Repair or replace any defective wiring or components as necessary, and then recheck the throttle body and TPS.
Connect the scanner to the diagnostic connector, retrieve all stored trouble codes, and make a note of them for future reference. It is also helpful to keep any related freeze frame data. These notes can be valuable if the stored code proves to be intermittent. Next, clear the codes and take the vehicle for a test drive. If the code is reset, continue with the diagnosis. If it is not reset, the condition may need to worsen before an accurate diagnosis can be made. Operate the vehicle normally until the PCM enters readiness mode or the code is reset.
Proceed by checking for any technical service bulletins (TSB) that apply to the specific malfunction and vehicle in question. Consult your vehicle information source for information contained in the appropriate TSB, as it can be particularly helpful when dealing with an intermittent condition.
The scanner data stream may provide useful information regarding glitches and inconsistencies in the throttle position sensor. Narrowing down the scanner data stream to display only relevant data will yield a more accurate response.
If no glitches are detected, use the DVOM to test the TPS. Connecting the appropriate test leads to the ground and signal circuits of the DVOM will provide access to live data. Observe the DVOM display while manually operating the throttle. Look for voltage glitches as the throttle is slowly actuated from the closed position to wide open throttle. Voltage typically ranges from 0.5 volts at closed throttle to 4.5 volts at wide open throttle. If any glitches or inconsistencies are detected, suspect that the sensor being tested is defective or misadjusted.
Additional diagnostic notes:
