P01EE

Code

Generic P — Powertrain

Engine Coolant Heater B Control Circuit High

Brand: Generic

Type: P — Powertrain

Views: UK: 22 EN: 32 RU: 27

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Page language: EN

Causes

Open or shorted wiring in the coolant heater B control circuit
Corroded, loose, or damaged connector at the heater, relay or PCM
Failed coolant heater element (open or internally shorted)
Stuck or failed relay controlling heater B
Power side shorted to battery voltage (feed) or backfeed into the control output
Faulty PCM/ECM driver transistor or internal module fault

Symptoms

Malfunction indicator lamp (MIL) or check engine light illuminated
Engine coolant heater may not operate when commanded
Longer engine warm-up times, especially in cold conditions
Possible reduced fuel economy during cold start
Stored or pending trouble code(s) related to coolant heating circuit

What to check

Retrieve freeze/frame and readiness data; verify whether code is current, pending, or historic
Visual inspection of wiring and connectors for damage, corrosion, or loose terminals at the heater, relay, fuse, and PCM
Check fuses and relays related to the coolant heater circuit
Backprobe the PCM/heater control connector and measure voltages while commanding the heater ON and OFF
Measure heater element resistance at the heater connector (compare to manufacturer spec)
Check for continuity to ground and for shorts to battery voltage in the control and power circuits

Signal parameters

Control output voltage at PCM when heater is OFF: should be low or near 0V (or high impedance depending on design) — consult service manual
Control output voltage when PCM commands heater ON: should switch between 0V (sink) and battery voltage or be modulated by PWM depending on application
Heater element resistance: usually low (single to tens of ohms); compare to vehicle spec
Supply (battery) voltage at fuse/relay: ~12–14.5 V with engine running
Expected PCM driver current when ON: varies by design (refer to OEM spec); abrupt high-voltage reading on control line when OFF indicates open load or short to battery

Diagnostic algorithm

Confirm the code and obtain freeze-frame/related codes. Clear the code and re-check to see if it returns.
Perform a thorough visual inspection of harness, connectors, and components related to coolant heater B (heater element, relay, fuse, grounds, PCM connector). Repair any obvious damage.
With ignition OFF, disconnect the coolant heater B connector and measure resistance of the heater element to ground. Compare to service specification; if open or out of range, replace the heater.
Check for continuity from the PCM control pin to the heater connector pin. Repair any opens or high-resistance connections.
Inspect and test the relay and fuse in the heater power circuit. Swap with a known-good identical relay if applicable.
With safe test setup, backprobe the PCM control output and monitor voltage while commanding the heater ON and OFF using a scan tool. Look for unexpected high voltages when the output is OFF (indicating a short to battery or open-load float).
Check for short to battery on the control circuit: disconnect connectors along the circuit and measure voltage at each point to localize the short/backfeed.
If wiring and heater test OK, test or substitute the PCM (only after confirming harness and components are good). Follow OEM procedures for PCM testing/replacement.
After repairs, clear codes and perform operational test under the conditions that originally set the code (cold start if applicable). Verify code does not return.

Likely causes

Disconnected or corroded connector at the coolant heater B
Open load in the heater element causing the control circuit voltage to float high
Short to battery voltage on the control circuit (backfeed through relay or wiring)
Failed relay or stuck contacts feeding the heater when PCM expects it off
Internal PCM driver failure

Fault status

⚠️ Status

Control circuit for coolant heater B reports abnormally high voltage to PCM. PCM may disable heater and store fault. Possible causes: wiring short to battery, open load, failed relay, connector corrosion, or PCM driver fault.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-2.0 hours

Repair manuals