P2B30

Code

Generic P — Powertrain

Fan 1 Stuck On

Brand: Generic

Type: P — Powertrain

Views: UK: 36 EN: 43 RU: 33

AI status

Completed

ready

Completed 100%

Page language: EN

Causes

Stuck or welded fan relay (stays closed)
Short circuit in fan control wiring to battery voltage
Low-side driver (MOSFET) or module output shorted to ground
Failed fan motor with internal short causing it to run
Control module/BCM/ECM software or hardware fault
Cooling temperature sensor or input commanding fan on erroneously

Symptoms

Cooling fan 1 runs continuously (engine off in some key positions or fan runs all the time)
Battery drain / parasitic draw when vehicle is parked
Engine running cooler than expected or temperature gauge low
AC compressor cycling differently or inconsistent HVAC performance
Unusual fan noise or vibration
Possible warning light or stored code present

What to check

Obtain freeze frame and live data with a scan tool: confirm fan status vs. commanded state
Visual inspection: check fan wiring harness, connectors, and ground for damage, corrosion or pinching
Inspect fan relay(s) and fuses related to Fan 1
With ignition on (engine off), measure voltage at the fan power feed and control pin at the fan connector
Command fan on/off with a scan tool: verify whether the module can change fan state and whether the fan responds
Disconnect fan connector: if fan continues to run, suspect an upstream short to power or an independent feed; if fan stops, suspect control circuit or module

Signal parameters

Normal battery supply voltage to fan: approximately 11–14.5 V (engine off or running as applicable)
Fan current draw (varies by vehicle): typically in the range of 5–30 A; consult vehicle specifications
Control signal types: either switched battery feed (relay) or low-side PWM/driver from module; PWM duty cycle 0–100% (frequency varies by manufacturer)
When commanded OFF: control line should show open/high impedance (no ground path) or 0% PWM duty; when commanded ON: control line will be actively driven (battery voltage or ground depending on architecture)

Diagnostic algorithm

Verify fault: read freeze frame and live data; confirm fan on status vs. requested state with a scan tool.
Visual inspection: check fan connector, wiring, fuses and relay for obvious damage, corrosion or aftermarket splices.
With ignition ON (engine off) and fan reported ON by PCM, measure voltage at the fan power feed and control pin. If power is present and control pin indicates command OFF, suspect shorted power feed or bypassed relay.
Command fan OFF/ON with scan tool and observe: if the PCM commands OFF but fan remains ON, disconnect the fan connector. If fan still runs when disconnected, there is a power feed short or another component powering the fan; if fan stops when disconnected, fault is in control circuit or module.
Check relay operation: remove/inspect/bench-test or swap with identical known-good relay. Replace if relay contacts are stuck.
Test fan motor by applying battery directly (bench test) to confirm motor does not self-run when power removed and to measure current draw. Excessive current indicates internal motor fault.
Use a lab scope to inspect the control output from the module for abnormal voltage (short to ground or battery, stuck logic).
Inspect/repair wiring harness: repair any chafed wires, pinched insulation, or water intrusion; replace connectors as needed.
Check temperature sensor inputs and other inputs that could command fan on (AC pressure switch, A/C command) and repair if they are falsely commanding running state.
If wiring, relay, and fan motor verify good but control output remains abnormal, consider module replacement or software reflash per manufacturer guidance.
After repairs, clear codes and perform a road test/temperature cycle to confirm the fault does not return.

Likely causes

Fan relay contacts welded closed or relay stuck mechanically
Power feed shorted directly to fan motor feed (constant 12V)
Control transistor inside module failed low (grounded) causing continuous operation
Fan motor bearing/seized condition causing unusual current draw but still powered
Faulty coolant temperature sensor or input commanding continuous cooling

Fault status

⚠️ Status

Fan 1 Stuck On — control module detects Fan 1 running continuously when it should be off. Potential electrical fault, relay, motor, wiring, or module issue.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0-2.5 hours