P0918 code definition
In vehicles equipped with automatic transmissions, a P0918 code means that the powertrain control module (PCM) has registered an intermittent fault in the transmission shift mechanism range circuit, particularly in regard to a specific lever position. The PCM uses data from the transmission range sensor, in order to control engine RPMs, fuel metering, ignition timing and other drivability factors.
What the P0918 code means
For most vehicles, a universal resistance level of 8 ohms is the norm in this particular circuit. Any fluctuation of greater than 10 percent (higher or lower) will result in a P2A00 code and an illuminated malfunction indicator lamp (MIL). Heater circuit voltage should be consistent with battery voltage, and any 10 percent fluctuation can result in a stored trouble code as well. Closed-loop O2 sensor readings that remain constant for 8 seconds or more can also result in a stored code and illuminated MIL.
What causes the P0918 code?
In most cases, a P0918 code is due to a failed transmission range sensor or an out-of-adjustment transmission range sensor. The code is specifically for an intermittent problem, so in many cases a P0918 code is due to failed, loose, damaged or corroded wiring or contacts.
What are the symptoms of the P0918code?
- Harsh shifts
- Failure to shift
- Limp-in mode
- Poor fuel economy
How does a mechanic diagnose the P0918 code?
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 over the shaft for the transmission sensor, where the lever slides along a row of contacts. When the shift lever is moved, this range sensor pivots and is moved to different contacts.
The contacts send varying levels of resistance to the PCM, according to the position of the shift lever. The PCM reads these differing levels of resistance and voltage as the gear selected at the shifter, and acts on this information to determine shift points, engine ignition timing, fuel metering and other functions. The PCM also determines the proper gear for the transmission according to information on engine load, RPMs other factors.
- Go over all related wiring, connectors and components and repair/replace any open, shorted, corroded or damaged wiring found. Retest the system. If all wiring, connectors and components check, connect the scanner to the diagnostic port and record any stored trouble codes.
- Check the transmission range sensor for battery voltage/ground signals.
- If either ground or battery voltage circuits check as “open,”, check for continuity/resistance in both circuits using the DVOM. Remember to disconnect any related control modules to avoid damage.
- Using a factory schematic, test any related circuits and the sensor itself for resistance/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.
Common mistakes when diagnosing the P0918 code
Often, technicians replace the entire transmission range sensor when adjustment would have been sufficient. In some cases, technicians have even been known to condemn the transmission unnecessarily.
How serious is the P0918 code?
A P0918 code can prevent a transmission from shifting out of a gear, and can put the vehicle in limp-in mode, meaning it will barely be drivable at all.
What repairs can fix the P0918 code?
Repair or replacement of:
- Transmission range sensor
- Corroded, loose or faulty wiring
Additional comments for consideration regarding the P0918 code
A P0918 code can accompany recent transmission work. Check the range sensor’s wiring for corrosion or damage and check the sensor for proper adjustment. When installing the sensor, use thread locking compound to ensure the proper torque retention for the mounting bolts.
Need help with a P0918 code?
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This article originally appeared on YourMechanic.com as P0918 Gear Shift Position Circuit – Intermittent Malfunction and was authored by Jerry Renshaw.