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P0E78: Coolant Bypass Valve A Control Circuit Range/Performance

Severity
Medium
System
Vehicle Systems
Last reviewed: Last updated:

Methodology: We combine code standards with complaint and reliability patterns, then review for clear, vehicle-first diagnosis steps.

Sources: SAE/OBD-II definitions, manufacturer service information, and public reliability reports (including NHTSA where applicable).

Limits: Guidance is informational and may not match every model-year or revision. Confirm with the official manual and diagnostics before replacing parts. For safety-critical or electrical work, use a qualified technician.

What Does P0E78 Mean?

P0E78 is a diagnostic trouble code indicating: Coolant Bypass Valve A Control Circuit Range/Performance. This code relates to the vehicle systems system. The vehicle's computer detected a condition outside normal operating parameters and stored this code.

Symptoms of P0E78

Common Causes

Frequently Asked Questions

What does P0E78 mean?
P0E78 indicates: Coolant Bypass Valve A Control Circuit Range/Performance. The vehicle's computer has detected that the Coolant Bypass Valve A is not operating within its expected parameters and stored this diagnostic trouble code.
Can I drive with code P0E78?
You can drive short distances for essential trips, but schedule a diagnosis soon. Driving with P0E78 for extended periods may cause additional problems.
How much does it cost to fix P0E78?
Repair costs for P0E78 typically range from $50 to $250, depending on the root cause. Simple wiring or connector repairs are on the lower end, while component replacement costs more. A proper diagnosis ($80–$150 at most shops) will identify the exact cause before committing to expensive parts.

What To Do Next

Possible Fixes

  • 🔧 Inspect and clean Coolant Bypass Valve A
  • 🔧 Replace degraded Coolant Bypass Valve A
  • 🔧 Check for related mechanical issues affecting readings
  1. 1
    Find your vehicle above

    Click your make and model for real owner reports and common causes specific to your vehicle.

  2. 2
    Check for recalls

    Go to nhtsa.gov/recalls and enter your VIN. Free repairs if covered.

  3. 3
    Get a professional diagnosis

    A code alone doesn't identify the exact failed part. A diagnostic ($50–$150) pinpoints the root cause.

Related Codes

P0E00 Generator Phase U Current Sensor Circuit P0E01 Generator Phase U Current Sensor Circuit Range/Performance P0E02 Generator Phase U Current Sensor Circuit Low P0E03 Generator Phase U Current Sensor Circuit High P0E04 Generator Phase V Current Sensor Circuit P0E05 Generator Phase V Current Sensor Circuit Range/Performance P0E06 Generator Phase V Current Sensor Circuit Low P0E07 Generator Phase V Current Sensor Circuit High P0E08 Generator Phase W Current Sensor Circuit P0E09 Generator Phase W Current Sensor Circuit Range/Performance