P2C42

Code

Generic P — Powertrain

Fan 4 Performance/Stuck Off

Brand: Generic

Type: P — Powertrain

Views: UK: 24 EN: 38 RU: 15

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Page language: EN

Causes

Failed cooling fan motor (open, seized, high internal resistance)
Blown fuse or faulty fan relay
Open, shorted, corroded or disconnected wiring/connector between fan and control module/relay
Faulty fan control module or body/control module (BCM/PCM) output driver
Faulty temperature sensor or erroneous input preventing command
Mechanical obstruction preventing fan rotation

Symptoms

Cooling fan (Fan 4) does not run when engine is hot or when commanded by A/C
Engine or A/C may overheat or run hotter at idle/low speed
Reduced air conditioning performance at low speeds
MIL/Check Engine Lamp illuminated with P2C42 stored
Visible fan not spinning or spins slowly
Possible electrical burning smell if shorted

What to check

Read and record freeze frame and any related codes with a capable scan tool (include body/PCM modules)
Visual inspection of fan, shroud, wiring harness and connectors for damage, corrosion, or disconnection
Check fuse(s) and relay(s) for the fan circuit
Attempt to command Fan 4 ON with a scan tool; observe fan operation and module response
Measure voltage at the fan power pin while the fan is commanded ON
Measure continuity and resistance of fan motor windings with connector disconnected

Signal parameters

Expected supply voltage at fan power terminal when commanded ON: ~11–14 V (battery voltage) or a switched/pulsed supply depending on system
Expected ground continuity from fan ground terminal to chassis: near 0 Ω (very low resistance)
Typical fan motor winding resistance (varies by vehicle): roughly 0.2–3 Ω (low ohms) — check manufacturer spec
Typical running current (varies by fan size): approximately 5–25 A; significantly higher or open circuit indicates fault
If PWM controlled: control signal frequency commonly in the tens to low hundreds of Hz; duty cycle varies 0–100% when commanded
When commanded OFF: control line should be open or inactive per manufacturer design

Diagnostic algorithm

Connect scan tool: read P2C42 and any related codes; note freeze frame (engine temp, vehicle speed, A/C status).
Visual inspection: check fan blades, shroud, wiring harness, connector pins for corrosion, damage, or foreign objects. Repair physical issues first.
Check fuse(s) and relay(s): inspect and swap a known-good relay if available. Replace blown fuses.
Functional command: with engine safe to run (or key ON for A/C command), command Fan 4 ON via scan tool and observe. If fan runs, refer to intermittent wiring or control logic. If not: continue.
Voltage test: back-probe fan power and ground at connector while commanding ON. Verify battery voltage on power feed or expected PWM signal and good ground. If power present and ground good but fan does not run, suspect fan motor or internal fan control.
Motor resistance and bench test: disconnect fan and measure winding resistance. Compare to spec. Apply fused 12 V directly to motor to confirm operation and measure current. Replace fan if it fails to run or draws excessive current.
Wiring checks: if no voltage present when commanded, trace wiring back to relay/control module. Check continuity, shorts to ground/power, and connectors. Repair damaged wiring or connectors.
Control module/relay tests: verify relay control circuit and module output using scope or test lamp as appropriate. Replace relay or module if proven faulty and wiring is good.
Check related sensors: verify coolant temp sensor and A/C status inputs so module is correctly commanding fan. Replace sensor if out of spec.
Clear codes and perform road/idle test to confirm repair; monitor temps and fan operation under load.