P2161 Vehicle Speed Sensor B Intermittent

OBD-II DTC Datasheet

Vehicle speed sensor "B" Intermittent / erratic / high

What does this mean?

This Diagnostic Trouble Code (DTC) is a generic transmission code, which means it applies to all 1996 vehicles (Ford, Dodge, GMC, Chevy, etc.). Although general in nature, the specific repair steps may differ depending on the brand / model.

When stored code P2161 is displayed, it means the powertrain control module (PCM) has detected a voltage input signal from the vehicle speed sensor (VSS) B that is intermittent, erratic, or excessive. The B designation usually refers to the secondary VSS in a system that uses multiple vehicle speed sensors.

OBD II vehicle speed sensors are generally electromagnetic sensors that use a specific type of jet wheel or gear that is mechanically attached to an axle, transmission / transfer case output shaft, differential transmission, or drive shaft. As the shaft rotates, the metal ring of the reactor rotates. The ring of the reactor completes the circuit with the stationary electromagnetic sensor as the reactor passes in close proximity to the electromagnetic tip of the sensor. The slots between the teeth of the reactor ring create breaks in the sensor circuit. The combination of circuit completions and interrupts is recognized by the PCM (and possibly other controllers) as voltage waveform patterns.

The PCM monitors vehicle speed using input from one or more vehicle speed sensors. The PCM compares the input from the VSS with the inputs of the Antilock Brake Control Module (ABCM) or Electronic Brake Control Module (EBCM). The primary VSS input (B) is likely to be initiated by the VSS in the transmission, but the secondary VSS input can be monitored by one or more wheel speed sensors.

If the PCM detects an intermittent, erratic, or high input voltage signal from the primary VSS, a P2161 code will be stored and the malfunction indicator lamp may illuminate. An unstable, unstable, or high voltage input may be the result of an electrical or mechanical problem.

Code severity and symptoms

Because conditions that could cause the P2161 code to persist can create drivability and ABS problems, they should be classified as serious and addressed with some degree of urgency.

Symptoms of a P2161 code may include:

Unstable operation of the speedometer / odometer
Irregular gear shifting patterns
Other transmission and ABS codes can be stored
Emergency engine lamp, traction control lamp or anti-lock brake system lamp illuminates
Unexpected activation / deactivation of traction control (if equipped)
In some cases, the ABS system can fail.

reasons

Possible reasons for this code:

Excessive accumulation of metal debris on the speed sensor / s
Defective wheel speed or vehicle speed sensor.
Cut or otherwise damaged wiring harnesses or connectors (especially near speed sensors)
Damaged or worn teeth on the reactor ring.
Defective PCM, ABCM or EBCM

Diagnostic and repair procedures

I will need a diagnostic scanner, a digital volt / ohmmeter (DVOM), possibly an oscilloscope and a reliable source of vehicle information to diagnose the P2161 code. A scanner with built-in DVOM and oscilloscope would be ideal for this diagnosis.

I like to start diagnostics with a visual inspection of the system wiring, speed sensors, and connectors. I would repair open or shorted circuits as needed and remove excess metal debris from damaged sensors. If removal of the sensor is possible, I would also check the integrity of the entire reactor ring at this time.

Then I connected the scanner to the car diagnostic port and got all stored DTCs and freeze frame data. Write down this information as it may be helpful as your diagnosis progresses. Now clear the codes and test drive the vehicle to see if symptoms persist and / or cleared.

A trick many professional technicians use is to search your vehicle information source for the correct technical service bulletins (TSB). If you find a TSB that matches the symptoms and stored codes of the vehicle in question, the diagnostic information it contains is likely to help diagnose the P2161 correctly.

Observe the wheel speed and / or vehicle speed (using the scanner data stream) while testing the vehicle. By narrowing the data stream to display only the relevant fields, you can improve the speed and accuracy of delivering the data you want. Irregular, erratic, or high readings from VSS sensors or wheel speed can lead to wiring, electrical connector, or sensor problems by narrowing the overall system fault area.

Use the DVOM to perform a resistance test on the sensor in question after you pinpoint the problem area. Check with your vehicle's information source for manufacturer recommendations for testing VSS and replacing sensors that are out of specification. The oscilloscope can be used to acquire real-time data from each individual VSS by probing the sensor signal wire and the sensor ground wire. The transmission must be in good working order, therefore a reliable jack or vehicle will be required to safely perform this type of test.

Vehicle speed sensors are often damaged as a result of regular transmission maintenance, and wheel speed sensors (and sensor wiring harnesses) often break when the brakes are repaired. If a P2161 code is displayed (immediately after repair), suspect a damaged sensor harness or sensor.

Additional diagnostic notes:

When performing a loop resistance and continuity test with the DVOM, always disconnect the electrical connectors from the associated controllers - failure to do so may result in damage to the controller.
Use caution when removing transducers from transmission cases (for testing) as hot transmission fluid can be harmful.

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