Error Code P0918 is defined as Gear Shift Position Circuit – Intermittent Malfunction. 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 the present. Specifications on the definition, troubleshooting, and repairs, of course, vary from one make and model to another.
For vehicles equipped with automatic transmission, this code means the powertrain control module (PCM) has determined an intermittent fault in the transmission shift mechanism range circuit, specifically to the particular lever position. To control engine RPMs, fuel metering, ignition timing, and other factors regarding the vehicle’s drivability, the PCM uses data from the transmission range sensor.
For most vehicles, the resistance level is 8 ohms in this specific circuit. Any changes more than 10% (higher or lower) will lead to error code P2A00 and activate the check engine light. Subsequently, the heater voltage circuit must be consistent with the battery voltage, and any fluctuation of around 10% can result in this trouble code. Closed-loop O2 sensor readings that remain constant for 8 seconds or more can also result in a stored code and illuminated MIL.
- Harsh or no shifting condition
- Increased fuel consumption
- Vehicle may enter “Limp Mode”
In most cases, the cause for this code is a failed transmission range sensor or transmission range sensor that is out of adjustment. And since this specific error code is an intermittent problem. In many cases, it can be caused by damaged, corroded, or loose contacts or wirings.
How to Check
As with most cases, you will need a digital volt/ohmmeter (DVOM) and an OBD-II scanner in diagnosing this code.
Many vehicles, such as Ford models, are equipped with a variable resistance transmission range sensor. The switch can be found over the shaft for the transmission sensor, where the lever can slide along a row of contact points. Every time the shift lever is moved, the range sensor pivots and is moved to a different contact.
The PCM receives varying levels of resistance from these contacts, depending on the position of the shift lever. The PCM reads these differing resistance levels and voltage as the gear selected at the shifter and works on the given information to determine the shift points, fuel metering, engine ignition timing, and other functions. Subsequently, the PCM also determines the appropriate gear for the transmission according to the engine loads, RPM, etc.
Proceed on the diagnosis by checking over all related wirings, connectors, and components. Repair or replace as necessary (repair or replace any corroded, shorted, or damaged wires). Retest the system. If all connectors and wirings are in good condition, connect the scanner to the vehicle’s diagnostic port and record all the stored error codes.
Next, check the transmission range sensor for the battery voltage or ground signals.
If either ground or battery voltage circuits check as “open”, inspect both circuits for continuity or resistance using the DVOM. To avoid damage, make sure you disconnect any related control modules.
Using the factory schematic, test all related circuits. Also, check the sensor for resistance or continuity. Compare to factory specs and replace/repair any circuits, connectors, or components that do not comply with specs.
Clear codes and retest the system.
How to Fix
Common repairs for this code include:
- Repair or replacement of transmission range sensor
- Repair or replacement of corroded, defective, or loose wirings
Many times, technicians replace the whole transmission range sensor when a simple adjustment would have been enough.
Since this code can cause vehicle problems on shifting and even put the vehicle in limp mode, then it must be addressed as soon as possible.