P0998

What it means

P0998 is the generic code for a low signal in the control circuit of shift solenoid F in the automatic transmission. The transmission control unit commands the solenoid and monitors the circuit, and it saw a voltage lower than expected, which points to a short to ground, a wiring fault or a failing solenoid or driver. Which gears or functions solenoid F controls depends on the transmission, so check the model-specific information.

Symptoms

• Gearbox warning light or malfunction indicator lamp on
• Gearbox stuck in one gear (limp mode)
• Harsh, delayed or flared gear changes
• Missing or unavailable gears
• Poor fuel economy or reduced performance
• Failed or erratic shifts under load

Possible causes

• Wiring chafed or shorted to ground in the solenoid circuit or transmission harnesslikely
• Faulty shift solenoid F (internal short or low resistance)likely
• Damaged, corroded or contaminated connector at the transmission or control unitlikely
• Fluid contamination or metal debris affecting the solenoid or valve bodypossible
• Low or degraded transmission fluid affecting the solenoid and its operationpossible
• Internal fault in the transmission control unit driver circuitrare
• Outdated or faulty control unit software, where a manufacturer bulletin confirms itrare

How to diagnose

1. Read all stored and pending codes and note the freeze frame data, including gear, temperature and speed at the time of setting
2. Check the transmission fluid level, condition and smell, following the manufacturer's procedure for the model
3. Visually inspect the wiring and connectors between the transmission and control unit for chafing, heat damage, water or corrosion
4. Check the solenoid circuit for voltage and short to ground at the connector, using the wiring diagram for the model
5. Measure the solenoid resistance and compare it with the manufacturer's specification
6. Wiggle-test the harness with the circuit monitored to find intermittent faults
7. Inspect the fluid and pan for debris, and check the valve body and solenoid if the fluid is contaminated
8. Check for relevant service bulletins or software updates for the vehicle

How to fix

• Repair or replace damaged wiring and ensure it is properly routed and secured
• Clean or replace corroded or damaged connectors and terminals
• Replace shift solenoid F, or the solenoid pack, if it is out of specification
• Correct the fluid level, or change the fluid and filter where it is degraded or contaminated
• Repair or replace the valve body if debris or wear is found
• Replace or reprogram the control unit only after the wiring and solenoid are proven good, and a confirmed fault or update applies

Can I keep driving?

Nearby codes

• P0997GenericShift Solenoid F Control Circuit Range/Performance
• P0999GenericShift Solenoid F Control Circuit High