Shift Timing Solenoid A Low
Code P0787 indicates the transmission shift timing solenoid A is receiving a low voltage signal or has low electrical resistance, preventing proper solenoid operation. This affects automatic transmission shift quality and timing, as the solenoid controls hydraulic pressure for gear transitions.
What You Might Notice
- Stuck in a single gear or limp mode
- Erratic or delayed shifting
- Harsh or hard shifting between gears
- Transmission slippage
- Poor acceleration and overall performance
Most Common Causes
- 1
Faulty shift timing solenoid A
The solenoid coil has failed electrically or mechanically, causing low resistance or inability to generate proper magnetic field for valve actuation.
- 2
Wiring or connector issues
Corroded, loose, or damaged wiring and connectors between the ECM and solenoid create resistance or voltage drop that prevents normal solenoid operation.
- 3
Low transmission fluid
Insufficient fluid level affects solenoid cooling and hydraulic response, potentially causing voltage irregularities in the solenoid circuit.
- 4
Engine Control Module (ECM) fault
A defective ECM output driver or circuit board issue can fail to supply adequate voltage or current to the shift solenoid A circuit.
How to Diagnose It
- 1
Check Faulty shift timing solenoid A — The solenoid coil has failed electrically or mechanically, causing low resistance or inability to generate proper magnetic field for valve actuation.
- 2
Check Wiring or connector issues — Corroded, loose, or damaged wiring and connectors between the ECM and solenoid create resistance or voltage drop that prevents normal solenoid operation.
- 3
Check Low transmission fluid — Insufficient fluid level affects solenoid cooling and hydraulic response, potentially causing voltage irregularities in the solenoid circuit.
- 4
Check Engine Control Module (ECM) fault — A defective ECM output driver or circuit board issue can fail to supply adequate voltage or current to the shift solenoid A circuit.
How to Fix It
- 1
Inspect and replace shift timing solenoid A
Locate the solenoid on the transmission, test it for proper resistance with an ohmmeter, and replace if out of specification. Ensure proper seating of the replacement.
- 2
Check and repair wiring and connectors
Inspect the solenoid harness and connector for corrosion, bent pins, and loose connections. Clean corroded connections and repair or replace damaged wiring as needed.
- 3
Check transmission fluid level and condition
Verify fluid level is at proper mark and fluid color is red without burnt odor. Top up with manufacturer-specified ATF or perform fluid service if dirty.
- 4
Have ECM tested or replaced if needed
If solenoid, wiring, and fluid are acceptable, have a professional test the ECM output circuits with a scope. Replace ECM only if confirmed faulty by diagnostics.
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