Error Code P0708 is defined as Transmission Range Sensor “A” Circuit High. This is a generic trouble code, meaning it applies to all vehicles equipped with the OBD-II system, especially those made since 1996 up to present. Specifications on the definition, troubleshooting, and repairs, of course, vary from one make and model to another.
This code refers to the transmission control system, and a type “B” code, which means the PCM (powertrain control module, also known as ECM or engine control module in other vehicle makes) or TCM (transmission control module) will not light up until the condition to set the code are detected on two consecutive key sequences (key on-off, off-on).
Sometimes called inhibitor switch, transmission range sensor is both used by the PCM or TCM to determine the position of the shift lever. If it receives a signal indicative of two different positions of the gear at the same time within 30 seconds (or more), then this error code will be set. If this happens twice in a row, then it will light up the Check Engine light and cause the transmission to go to “limp-home” mode or “fail-safe” mode.
Other related transmission range sensor error codes include:
- Transmission slippage
- Hard shifting or transmission unable to shift at all
- Defective range sensor
- Misadjusted transmission range sensor
- Misadjusted transmission (shift cable/linkage)
- Damaged wiring, faulty or disconnected wiring associated with transmission range sensor
- Defective PCM (rare)
How to Check
The transmission range sensor gets 12V signal from the ignition switch, and then sends the signal back to the PCM/TCM that is appropriate for the chosen position of the gear shifter.
In most cases, the most common cause for this code is misadjusted shift cable/linkage or faulty range sensor.
As with most codes, you will need a scan tool to diagnose this error code. But if that’s not available, then there are a few things you can check.
Put the key in KOEO (key on engine off). Using the DVOM (digital voltohmmeter), probe the connected sensors to check the return signal circuit individually. Have an assistant shit to each gear one at a time. Each signal circuit must have a voltage in one position only. If there’s voltage in of the circuit in more than one gear position, then you can suspect a defective range sensor.
In many cases, the PCM rarely fails. This, however, doesn’t mean it’s not a possibility. Faulty PCM can be a result of a short circuit in a range sensor. Thus, if you suspect a faulty PCM problem, make sure you check the damage before installing a new one to avoid causing the same problem.
How to Fix
Depending on the diagnosis, common repairs for this code include:
- Replacement of transmission range sensor
- Repair or replacement of wiring associated with transmission range sensor
- Adjusting the transmission range sensor
- Replacement of ECM
Error Code P0708 is quite a serious problem as it can cause both drivability issues and lead to serious transmission damage.
Some vehicles come equipped with a “fail-safe” mode that will put the engine in limited power and speed to keep the transmission damage at a minimum.