Definition of Code P0918
In vehicles equipped with automatic transmissions, a code P0918 means that the Powertrain Control Module (PCM) has recorded an intermittent fault in the gear shift mechanism range circuit, particularly regarding a specific lever position. The PCM uses data from the transmission range sensor to control engine speed, fuel dosage, ignition timing, and other driving factors.
What does code P0918 mean?
For most vehicles, a universal resistance level of 8 ohms is standard in this particular circuit. Any fluctuation greater than 10% (higher or lower) will result in a P2A00 code and a Malfunction Indicator Light (MIL). The heater circuit voltage must be consistent with the battery voltage, and any 10% variation can also lead to a stored fault code. Closed-loop O2 sensor readings that remain constant for 8 seconds or more can also result in a stored code and an illuminated MIL.
What causes code P0918?
In most cases, a code P0918 is due to a faulty transmission range sensor or an unadjusted transmission range sensor. The code is specifically for an intermittent problem, so in many instances, a code P0918 is caused by faulty, loose, damaged, or corroded wiring or contacts.
What are the symptoms of code P0918?
- Harsh shifting
- Failure to shift
- Limp-in mode
- Poor fuel economy
How does a mechanic diagnose code P0918?
A technician will need a good quality OBD-II scanner/code reader and a digital volt/ohmmeter (DVOM).
Most vehicles, especially Ford models, are designed with a variable resistance transmission range sensor. This switch is located on the transmission sensor shaft, where the lever slides along a row of contacts. When the gear lever is moved, this range sensor pivots and is moved to different contacts.
The contacts send different resistance levels to the PCM, depending on the gear lever position. The PCM reads these varying resistance and voltage levels as the selected gear ratio on the shift lever and acts on this information to determine shift points, engine ignition timing, fuel dosage, and other functions. The PCM also determines the appropriate transmission ratio based on engine load information and other factors.
Review all cables, connectors, and related components and repair/replace any open, shorted, corroded, or damaged wiring. Retest the system. If all cables, connectors, and components check out, connect the scanner to the diagnostic port and record all stored fault codes.
Check the transmission range sensor for battery voltage/ground signals.
If the ground or battery voltage circuits check as “open,” verify continuity/resistance in both circuits using the DVOM. Remember to disconnect all related control modules to prevent damage.
Using a factory diagram, test all associated circuits and the sensor itself for resistance/continuity. Compare with factory specifications and replace/repair any circuits, connectors, or components that do not meet specifications.
Clear the codes and retest the system.
Common mistakes when diagnosing code P0918
Often, technicians replace the entire transmission range sensor when adjustment would have been sufficient. In some cases, technicians have even been known to unnecessarily condemn the transmission.
How severe is code P0918?
A code P0918 can prevent a transmission from shifting and may put the vehicle in limp mode, meaning it will be barely drivable.
What repairs can fix code P0918?
Repair or replacement of:
Transmission range sensor
Corroded, loose, or faulty wiring