Shift Timing Solenoid B Malfunction
The P078A code indicates a malfunction in the shift timing solenoid B, which is part of the transmission's hydraulic control system. This solenoid regulates fluid pressure to control gear shift timing. When it fails, the transmission may shift erratically, slip, or get stuck in a gear. The issue can stem from electrical faults, low fluid, or internal transmission wear.
01. Most Common Causes
- Faulty shift timing solenoid B
- Low or contaminated transmission fluid
- Wiring or connector issues in the solenoid circuit
- Internal transmission mechanical failure
02. Symptoms You Will Notice
- Harsh or delayed shifts
- Transmission slipping
- Check Engine Light illuminated
- Transmission stuck in limp mode
03. Step-by-Step Diagnosis
Step 1: Scan for codes and verify P078A is present.
Step 2: Check transmission fluid level and condition; top off or replace if necessary.
Step 3: Inspect wiring and connectors for damage or corrosion; repair as needed.
Step 4: Test solenoid resistance with a multimeter; replace if out of spec.
Step 5: If solenoid and wiring are good, perform a transmission pressure test to identify internal issues.
04. Commonly Affected Makes
05. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended. Driving with a faulty shift solenoid can cause erratic shifting, transmission damage, or complete failure, leaving you stranded.
How much does it cost to fix?▼
Repair costs typically range from $150 to $400, including parts and labor. Solenoid replacement is often $50-$150 for the part plus 1-2 hours of labor.