What does it mean?
This diagnostic trouble code (DTC) is a generic powertrain code, meaning it applies to vehicles equipped with OBD-II. Although generic, specific repair steps may vary by make/model.
This is a generic powertrain diagnostic trouble code (DTC) in the transmission subgroup. It is a type “B” code, meaning the Powertrain Control Module (PCM) or Transmission Control Module (TCM) will not illuminate the Check Engine light unless the conditions for setting the code are present for two consecutive key cycles (key on-off, off-on).
The PCM/TCM uses the transmission range sensor, sometimes called the inhibitor switch, to identify which gear position the shift lever is in. The code definition itself explains the issue causing the code; the signal from the range sensor is not present all the time or is intermittently missing.
Symptoms
and severity of the code
After the second key cycle, the PCM/TCM will illuminate the Check Engine light and force the transmission into “Limp-home” or “fail-safe” mode. There will be a noticeable loss of power, more visible when taking off from complete stops. In this mode, the transmission starts in third gear, which is hard on the transmission’s internal clutches.
Based on my experience, this can cause severe internal damage to the transmission, so it should be fixed as soon as possible. Avoid using the vehicle until repairs can be made.
Causes
The possible
causes for this code being set are:
Faulty transmission range sensor
Faulty wiring
(Rarely) Faulty PCM or TCM
Diagnostic and Repair Procedures
The transmission range sensor receives a 12-volt signal from the ignition switch and then sends a 12-volt signal, on the appropriate circuit based on the gear position, to the PCM/TCM.
P0709 is set when the signal is missing at the PCM/TCM. A scan tool with live data capability is the most accurate way to diagnose this DTC, but if unavailable, here are some items that can be checked with a digital volt-ohmmeter (DVOM). Based on my experience, the most common cause of intermittent signal issues is related to wiring.
In this case, a close visual inspection of the transmission range sensor wiring harness and the internal contacts of the range sensor connector should be performed first and thoroughly. If anything is found suspicious during the inspection, repair the issue, clear the codes, and test the vehicle. If the DTC returns, set the DVOM to volts and probe the appropriate circuits at the PCM/TCM and “wiggle” the harness at and leading to the range sensor. If no intermittent voltage loss is seen on the multimeter, suspect a faulty range sensor.
Related Transmission Range Sensor Codes: P0705, P0706, P0709, P0709, and P0709