Error Code P06A8 is defined as Sensor Reference Voltage “C” Circuit Range/Performance. This is a generic trouble code, meaning it applies to all vehicles equipped with OBD-II system. This includes vehicles models from but not limited to, Chevrolet, Ford, Honda, etc. Specifications on the definition, troubleshooting, and repairs, of course, vary from one make and model to another.

If the vehicle stores Error Code P06A8, this means the PCM (powertrain control module, also known as ECM or engine control module in other vehicle makes) has determined a voltage signal that is out of range or a performance problem within a specific sensor that has been given the designation “C”. This sensor is usually associated with automatic transmission, transfer case, or one of the differentials. This code almost always comes with a more specific code. Thus, when diagnosing this code, it’s important to consult with a dependable vehicle information source (All Data DIY is a great choice) to determine sensor location (and function) as it relates to the vehicle in question.

If this code is stored and doesn’t come with other error codes, then you can suspect a programming error in the PCM. Other sensors must be diagnosed and repaired when dealing with this code, but the “C” circuit open issue must be kept in mind.

The reference voltage (usually 5V) is applied to the sensor in question through a switched (energized with the key on) circuit. There should also be a ground signal. And the sensor must be of either the variable resistance, or electromagnetic variety, and completes a specific circuit. As the pressure, temperature, and speed increases, the sensor resistance also decreases, and vice versa. As the resistance in the sensor changes with the conditions, it provides with the PCM and input voltage signal. If the PCM receives this input voltage signal, the circuit will be considered open, and the Error Code P06A8 will be stored.

In some cases, it may require multiple drive cycles before the Check Engine light lights up. With this, allow the PCM to enter readiness mode before considering any repairs as successful. Clear the codes after doing any repairs, and then take the vehicle for a test drive. If the PCM enters readiness mode, then the repair was successful. If the code comes back (resets), the PCM will not enter readiness mode, and the problem persists.

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Common Symptoms

The severity of symptoms for this code depends mostly with the sensor circuit experiencing the open condition. And as said earlier, this code almost always comes with other codes. Thus, it’s important to take note of those codes as well. Common symptoms for this code include:

  • Transmission shifting malfunction
  • Delayed (or no) engagement of the transmission
  • Transmission unable to shift between sport and economy modes
  • Transmission unable to shift between all-wheel and two-wheel drive modes
  • Lack of from the engagement front hub
  • Lack of engagement from the differential
  • Inoperative or erratic speedometer/odometer

Possible Causes

Several problems could lead to this code. Some of the most common causes are:

  • Open circuits and connectors
  • Blown or defective fuses and fusible links
  • Defective sensor power relay
  • Bad sensor

How to Check

To diagnose this code, you will need a diagnostic scanner, DVOM (digital volt/ohmmeter), and a dependable vehicle information source. A portable oscilloscope can also help.

Find the sensor in question using the vehicle information source for your specific vehicle. Check the fuses and fusible links with the circuit under a full load. Fuses that look normal where there is little load on the circuit often fail when the circuit is fully loaded. With this, blown fuses caused by short circuit must be replaced.

Then, inspect the sensor system’s wiring, including the harnesses and connectors. Repair or replace as necessary, especially burned wirings, connectors, or various components.

Next, connect the scanner to the diagnostic connector of the vehicle and retrieve all stored codes. Write them down, along with their freeze frame data. Then, clear the code and test drive the vehicle to see if they set immediately.

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If all system fuses are intact, and the code still resets immediately, then use the DVOM for test reference of the voltage and ground signal of the sensor in question. Typically, you can expect 5V and a common ground at the sensor connector.

If the voltage and ground single are present on the sensor connector, then continue testing the sensor resistance and continuity levels. Use the vehicle information source to get the right testing specs. Then, compare your findings. Sensors that are unable to comply with the specifications set by the manufacturer must be replaced.

Then, disconnect all related controllers from the system circuits before testing the resistance with the DVOM. If there are no reference voltage signals at the sensor, then disconnect all related controllers, and use the DVOM to check the circuit resistance and continuity between the sensor and the PCM. Open or shorted circuits must be replaced.

If the electromagnetic sensor is used, with a reciprocating signal, then use the oscilloscope to monitor live data. Pay attention to the glitches and completely open circuits.

How to Fix

Common repairs for this code include:

  • Repair or replacement of damaged electrical wirings and other related components
  • Replacement of damaged or defective control modules (varies depending on which control module have detected the fault)
  • Replacement of damaged (or defective) PCM

When Error Code P06A8 is normally associated with the drivetrain and is usually provided as support for more specific codes.

When diagnosing this code, it’s recommended to address them in order of which they are stored. Subsequent codes are usually symptoms of the bigger problem.

As this code affects the drivability of the vehicle, it is considered serious and is recommended to be addressed as soon as possible.