Transmission Fluid Pressure Sensor/Switch "E" Circuit Low
Code P0989 indicates the transmission fluid pressure sensor/switch circuit E is detecting a low voltage signal, suggesting an electrical fault in the sensor circuit or the sensor itself. This prevents the PCM/TCM from accurately monitoring transmission fluid pressure, which may cause transmission shifting issues or limp mode activation.
What You Might Notice
- Transmission shifting erratically or harshly
- Vehicle stuck in limp mode or failsafe gear
- Check engine light illuminated
- Delayed transmission engagement
- Reduced fuel economy due to forced gear selection
Most Common Causes
- 1
Shorted transmission fluid pressure sensor
The TFPS sensor has failed internally with a short to ground, preventing proper signal voltage from reaching the PCM/TCM and triggering the circuit low condition.
- 2
Short to ground in sensor signal wiring
Damaged, pinched, or corroded wiring in the TFPS signal circuit creates a direct path to ground, collapsing the voltage signal before it reaches the control module.
- 3
Loose or corroded sensor connector
Poor electrical contact at the transmission fluid pressure sensor connector prevents proper signal transmission due to oxidation or loose pin connections.
- 4
Faulty PCM/TCM
Rarely, a defective transmission control module may misinterpret a normal sensor signal as low voltage, though this is an unlikely cause compared to sensor or wiring faults.
How to Diagnose It
- 1
Check Shorted transmission fluid pressure sensor — The TFPS sensor has failed internally with a short to ground, preventing proper signal voltage from reaching the PCM/TCM and triggering the circuit low condition.
- 2
Check Short to ground in sensor signal wiring — Damaged, pinched, or corroded wiring in the TFPS signal circuit creates a direct path to ground, collapsing the voltage signal before it reaches the control module.
- 3
Check Loose or corroded sensor connector — Poor electrical contact at the transmission fluid pressure sensor connector prevents proper signal transmission due to oxidation or loose pin connections.
- 4
Check Faulty PCM/TCM — Rarely, a defective transmission control module may misinterpret a normal sensor signal as low voltage, though this is an unlikely cause compared to sensor or wiring faults.
How to Fix It
- 1
Replace transmission fluid pressure sensor
Remove the faulty TFPS sensor from the transmission, inspect the mounting surface for debris, and install a new sensor with proper torque specification. Verify correct sensor type for your transmission before installation.
- 2
Inspect and repair sensor wiring and connector
Trace the TFPS signal wiring from sensor to PCM/TCM, looking for damaged insulation, corrosion, or pinched areas. Repair or replace compromised wiring and clean or replace the connector terminals to restore proper electrical contact.
- 3
Clear code and perform test drive
After repairs, clear the diagnostic trouble code using a scan tool and road test the vehicle through various driving conditions to confirm transmission shifts smoothly and no codes return.
- 4
Program PCM/TCM if required
If the transmission control module was replaced, reprogram it with the correct vehicle calibration file and verify all transmission sensors are communicating properly before returning the vehicle to service.
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