Code Severity and Symptoms
Since conditions that can cause a stored P2161 code can create driving and ABS issues, it should be classified as severe and addressed with some degree of urgency.
Symptoms of a P2161 code may include:
- Erratic speedometer/odometer operation
- Irregular transmission shifting patterns
- Other transmission and ABS codes may be stored
- Illumination of check engine light, traction control light, or anti-lock brake light
- Unexpected activation/deactivation of traction control system (if equipped)
- ABS system may be rendered inoperative in some cases
Causes
Possible causes of this code include:
- Excessive metal debris accumulation on speed sensors
- Faulty wheel speed sensor or vehicle speed sensor
- Cut or damaged wiring harnesses or connectors (particularly near speed sensors)
- Damaged or worn teeth on a reluctor ring
- Faulty PCM, ABCM, or EBCM
Diagnostic and Repair Procedures
I would need a diagnostic scanner, digital volt/ohmmeter (DVOM), possibly an oscilloscope, and a reliable vehicle information source to diagnose a P2161 code. A scanner with built-in DVOM and oscilloscope would be ideal for this diagnosis.
I like to start my diagnosis with a visual inspection of the system wiring, speed sensors, and connectors. I would repair open or shorted circuits as needed and clean excessive metal debris from affected sensors. If sensor removal is possible, I would also check the integrity of the entire reluctor ring at that time.
Next, I would connect the scanner to the vehicle’s diagnostic port and retrieve all stored trouble codes and freeze frame data. Note this information as it may prove useful as your diagnosis progresses. Now clear the codes and test drive the vehicle to see if symptoms persist and/or if the code resets.
A tip many professional technicians use is to search the vehicle information source for applicable technical service bulletins (TSBs). If you find a TSB that matches the symptoms and stored codes of the vehicle in question, the diagnostic information it contains will likely help properly diagnose P2161.
Observe wheel speed and/or vehicle speed (using scanner data stream) during vehicle test drive. By reducing the data stream to display only relevant fields, you can increase the speed and accuracy of desired data delivery. Inconsistent, erratic, or high readings from VSS or wheel speed sensors can lead you to wiring, electrical connector, or sensor issues by narrowing the general area of system malfunction.
Use the DVOM to perform a resistance test on the sensor in question after identifying the problem area. Consult your vehicle information source for manufacturer recommendations regarding VSS testing and replace sensors that don’t meet specifications. The oscilloscope can be used to retrieve live data from each individual VSS by probing the sensor signal wire and sensor ground wire. The powertrain will need to be running, so jacking or lifting the vehicle will be necessary to perform this type of test safely.
Vehicle speed sensors are frequently damaged during routine transmission maintenance, and wheel speed sensors (and sensor wiring harnesses) are often broken during brake repairs. If a P2161 code appears (immediately after a repair), suspect a damaged sensor harness or sensor.
Additional Diagnostic Notes:
When performing circuit resistance and continuity tests with a DVOM, always disconnect electrical connectors from associated controllers – failure to do so could result in damaged controller
Be careful when removing sensors from transmission housings (for testing) as hot transmission fluid can be harmful