P2C40

Code

Generic P — Powertrain

Fan 4 Control Circuit High

Brand: Generic

Type: P — Powertrain

Views: UK: 19 EN: 32 RU: 25

AI status

Completed

ready

Completed 100%

Page language: EN

Causes

Short to battery voltage on fan #4 control circuit
Open or intermittent wiring/connector (corrosion, pin pushed out, chafe)
Failed cooling fan motor or internal short in fan assembly
Failed fan relay or fan control module (if separate)
Poor or detached ground on fan motor or control module
Faulty PCM or fan driver transistor

Symptoms

Cooling fan #4 may not respond to commands (won't turn ON)
Fan may run continuously or intermittently depending on wiring fault
Engine temperature rise or intermittent overheating under load/idle
A/C performance reduced (condensing efficiency lowered)
DTC P2C40 stored and possibly other related fan circuit codes present

What to check

Read freeze frame and live data with a scan tool; confirm which fan(s) commanded ON/OFF and status
Inspect fuses and relays for the cooling fan circuits
Visually inspect wiring and connectors at fan #4, fan relay/module, and PCM for damage, corrosion, or loose pins
Backprobe the fan #4 control connector and PCM control pin while commanding fan ON and OFF
Measure voltage at the control pin with fan commanded OFF (should be near battery voltage if low-side switch; see signal params) and with fan commanded ON (should be low near 0–1 V if PCM grounds the circuit)
Check ground circuit continuity for the fan motor and control module

Signal parameters

Battery voltage (key ON, engine OFF): ~12.0–14.5 V
Control circuit voltage when fan OFF: typically close to battery voltage (open/high) for low-side switch designs
Control circuit voltage when fan ON (PCM grounds circuit): typically
PWM control: when used, duty cycle 0–100% and frequency commonly 20–300 Hz (varies by manufacturer)
Typical fan motor resistance: a few ohms; inrush and running current vary by motor—expect several amps to tens of amps under load (vehicle-specific)

Diagnostic algorithm

Connect a capable scan tool, read and record freeze frame/live data. Clear codes and attempt to reproduce. Note when the PCM commands fan #4 ON/OFF.
Inspect fuses, fan relay(s), wiring harnesses and connectors for fan #4. Repair obvious damage or corrosion.
With ignition ON, backprobe the fan #4 control connector. With fan commanded OFF verify control voltage is at the expected level for that system (usually battery voltage for low-side control).
Command the fan ON via scan tool (or recreate conditions) and measure control pin voltage. If the circuit remains high instead of dropping near ground, suspect short to voltage or driver failure.
Disconnect fan connector; measure resistance of fan motor and perform a direct battery test to verify the fan motor spins and current draw is within spec. If motor is OK, fault likely upstream in wiring or driver.
Check ground continuity from fan negative to chassis and to PCM ground. Repair any poor ground.
Inspect/bench-test fan relay or fan control module if present. Substitute known-good relay/module if available.
If wiring and external components test OK and the control pin at the PCM still reads abnormally high when commanded ON, suspect PCM/fan driver failure. Confirm with manufacturer diagnostics before PCM replacement.
Repair/replace faulty wiring, connectors, relays, fan assembly, or PCM as required. Clear codes and road test to confirm the code does not return and fan operates correctly.

Likely causes

Short to battery in the fan #4 control feed or circuit (most likely)
Damaged connector or pin at fan or PCM (next likely)
Failed fan motor or internal driver in fan assembly
Failed external fan control relay or module
PCM/ECM driver fault (least common)

Fault status

⚠️ Status

PCM detected higher-than-expected voltage on Cooling Fan #4 control circuit (Circuit High). Fan control may be disabled; service the wiring, fan assembly, relay/module, or PCM as needed.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.8-2.0 hours