P01F8

Code

Generic P — Powertrain

Engine Coolant Heater A Control Circuit Driver Current/Temperature Too High

Brand: Generic

Type: P — Powertrain

Views: UK: 27 EN: 34 RU: 28

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Page language: EN

Causes

Short to ground or low resistance in the heater element or harness
Failed coolant heater element (internally shorted)
High current due to contaminated/shorted connector or wiring
Faulty relay or control module (PCM/driver) allowing excessive current
Poor ground or corroded connector increasing local heating
Incorrect replacement heater with wrong resistance or rating

Symptoms

Coolant may take longer to warm up (if heater used for cold-start conditioning)
Illumination of MIL/check engine light
Stored or pending fault P01F8
Possible blown fuse or repeated fuse failures related to heater circuit
Visible overheating or melting at connector or wiring in severe cases

What to check

Read freeze-frame and pending data; note conditions when code set (temperature, voltage)
Visual inspection of heater, harness, connectors for corrosion, damage, melting, or water intrusion
Check relevant fuses and relays for the heater circuit
Measure supply voltage to heater control relay or driver with key on
Measure resistance of heater element with it disconnected from harness
Inspect and measure ground integrity at heater ground point

Signal parameters

Supply voltage to heater relay/driver: approx. battery voltage (~11–14.5 V with engine off/running)
Heater element resistance (typical range varies by vehicle): often single-digit to low tens of ohms; significant deviation suggests open or short
Driver output current: should be within manufacturer spec (high current or short condition typically greater than expected operating current)
PCM sense/temperature input (if applicable): should change gradually with engine coolant temperature, not indicate an over-temperature fault at normal temps

Diagnostic algorithm

Retrieve freeze-frame data and confirm conditions (battery voltage, coolant temp, engine load) when P01F8 set.
Visually inspect the heater, wiring harness, connectors, and ground. Look for corrosion, melted insulation, pin damage or water intrusion.
With ignition off, disconnect the heater connector and measure heater element resistance. Compare to service spec or note if near zero (short) or infinite (open).
Check fuses and heater relay operation. With connector disconnected, verify relay clicks and that control circuit is switched by the PCM when commanded (use a scan tool to command if available).
Measure supply voltage at the heater connector with ignition on and while the heater is commanded on. Verify fused supply and voltage consistency.
Measure current through the heater circuit during operation using a clamp meter or inline ammeter. Compare to expected operating current. Excessive current indicates low resistance/short.
Inspect and test grounds related to the heater circuit. Repair any high-resistance or corroded grounds.
If heater element resistance and wiring are good but high current is still reported, consider a faulty driver/PCM or a shorted relay. Verify relay wiring and, if safe and guided by service manual, swap relay with identical known-good relay to test.
After repairs, clear codes and perform functional/road test to confirm code does not return. Recheck for heat damage signs that could recur.

Likely causes

Damaged/shorted heater element
Wiring short or low-resistance fault in heater harness or connector
Corroded connector or poor ground causing localized overheating
Faulty relay or driver in the PCM

Fault status

⚠️ Status

Engine Coolant Heater A Control Circuit Driver Current/Temperature Too High — PCM detected excessive current draw or over-temperature in the coolant heater A control circuit.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-2.0 hours