P2E78
Low Severity (Level 2)Hybrid/EV Battery Pack Coolant Temperature Sensor D Circuit Intermittent/Erratic
P2E78 usually means hybrid/EV Battery Pack Coolant Temperature Sensor D Circuit Intermittent/Erratic.
Can you still drive with P2E78?
⚠️Short-distance driving is usually OK, but have this diagnosed within a week to prevent further damage.
Typical repair cost: $50 – $300
Severity Level 2 — Low
This code indicates a minor issue that is unlikely to cause immediate driveability problems. You can typically continue driving but should have the vehicle inspected at your earliest convenience.
Common Symptoms
- No pattern to failure — seems random
- Temperature gauge working fine one moment, failing the next — classic intermittent fault
- Poor electrical connection causing intermittent signal dropouts
- Fault may be intermittent — code may clear itself and reappear
- Reduced vehicle functionality related to the engine coolant temperature sensor
Possible Causes
- Loose or corroded electrical connector in the engine coolant temperature sensor — vibration causes intermittent contact
- Internal failure in coolant temperature sensor — works when cold, fails when hot (thermal expansion breaks internal connection)
- Wiring harness partially broken inside the insulation — flex point in the harness causing intermittent open circuit
- Moisture in the engine coolant temperature sensor electrical connector causing intermittent shorts — common after car wash or heavy rain
Common Fixes
- Scan vehicle with a professional-grade OBD2 scanner to read all stored codes and freeze frame data — note the conditions when the code set ($35-93 at shop, free at auto parts store for basic scan)
- Visually inspect the engine coolant temperature sensor wiring harness and connectors — look for chafed wires, melted insulation, green corrosion, loose pins, or rodent damage (often free to check yourself, $58 diagnostic fee at shop)
- Replace coolant temperature sensor if testing confirms it has failed — use OEM quality, avoid the cheapest no-name aftermarket parts that fail in a year ($40-250)
- Check and replace any blown fuses in the engine coolant temperature sensor fuse circuit — if fuse blows again, there's still a short that needs to be found ($3-19 for fuses)
- Perform a wiggle test on the engine coolant temperature sensor wiring harness while monitoring live data — see if the fault returns when you move the harness at different points ($0-101 diagnostic labor)
Estimated Repair Cost
These are estimated costs based on generic repair data. Actual costs may vary depending on your vehicle, location, and labor rates.
Frequently Asked Questions
What does P2E78 mean?
P2E78 stands for "Hybrid/EV Battery Pack Coolant Temperature Sensor D Circuit Intermittent/Erratic". P2E78 usually means hybrid/EV Battery Pack Coolant Temperature Sensor D Circuit Intermittent/Erratic.
Can you drive with P2E78?
Short-distance driving is usually OK, but have this diagnosed within a week to prevent further damage.
How much does it cost to fix P2E78?
Repair costs for P2E78 typically range from $50 to $300, depending on your vehicle make, model, and local labor rates. Common fixes include: Scan vehicle with a professional-grade OBD2 scanner to read all stored codes and freeze frame data — note the conditions when the code set ($35-93 at shop, free at auto parts store for basic scan); Visually inspect the engine coolant temperature sensor wiring harness and connectors — look for chafed wires, melted insulation, green corrosion, loose pins, or rodent damage (often free to check yourself, $58 diagnostic fee at shop); Replace coolant temperature sensor if testing confirms it has failed — use OEM quality, avoid the cheapest no-name aftermarket parts that fail in a year ($40-250).
Will P2E78 clear itself?
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