P0787

What it means

P0787 is a generic powertrain code for a low signal in the shift/timing solenoid circuit in the automatic transmission. The transmission control unit commands the solenoid and monitors its circuit. It saw a voltage or current lower than expected, which points to a short to ground, high resistance or an open circuit, or a failed solenoid. Which gear shift or function the solenoid controls depends on the transmission, so check model-specific information.

Symptoms

• Gearbox warning light or engine management light on
• Harsh, delayed or flared gear changes
• Gearbox stuck in one gear (limp mode)
• Shifts at the wrong time or wrong road speed
• Poor fuel economy or higher engine revs than normal at cruising speed
• Gearbox may not engage some gears

Possible causes

• Wiring to the solenoid chafed and shorted to ground, or damaged inside the gearbox harnesslikely
• Faulty shift/timing solenoid (internal short or coil failure)likely
• Corroded, wet or loose connector at the gearbox or control unit, including fluid ingress in the internal harness connectorpossible
• Low, degraded or contaminated transmission fluid causing debris or solenoid wearpossible
• Low battery voltage or poor earth connections affecting the control unit and solenoid supplypossible
• Faulty transmission control unit or its driver circuitrare
• Outdated control unit software where the manufacturer has issued a known fix for this faultrare

How to diagnose

1. Read all stored and pending codes and the freeze frame data, noting road speed, gear, fluid temperature and battery voltage when the fault set
2. Check for related codes such as other solenoid, gear ratio or battery voltage faults, and check for any manufacturer service bulletins for the model
3. Check the transmission fluid level, condition and smell, following the procedure for that gearbox
4. Inspect the external gearbox wiring and connector for damage, rubbing, corrosion, moisture or fluid contamination
5. Test battery condition and charging voltage, and check the main earth connections
6. Measure the solenoid resistance at the connector and compare it with the manufacturer specification, and check for a short to ground
7. Check the wiring between the solenoid and control unit for continuity and shorts to ground or supply, then command the solenoid with a suitable scan tool and watch the response
8. If wiring and solenoid test good, check the control unit supply, earth and driver output before condemning the unit

How to fix

• Repair or replace damaged wiring or the internal gearbox harness and clean or replace faulty connectors
• Replace the faulty shift/timing solenoid, or the solenoid pack where it is not sold separately
• Correct the fluid level, or change the fluid and filter if it is contaminated, using the correct specification
• Repair battery, charging or earth faults
• Update or replace the transmission control unit software or the unit itself only if testing confirms it is faulty or a known software fault applies

Can I keep driving?

Nearby codes

• P0786GenericShift Timing Solenoid A Range/Performance
• P0788GenericShift Timing Solenoid A High