P1136 — control module intermittent circuit malfunction box fan

Causes

• Intermittent/open/short in fan control wiring harness
• Corroded or loose connector(s) at fan, relay or control module
• Failed fan motor or internal short
• Faulty fan relay or driver module
• Poor ground connection(s)
• Control module intermittent output or internal fault

Symptoms

• Cooling fan(s) fail to run when commanded or run erratically/intermittently
• Engine temperature climbs or AC performance reduced under load/idle
• Intermittent MIL/Check Engine lamp illumination
• Cooling fan may run continuously or not at all at times
• Possible electrical smell or visible corrosion/damage at connector

What to check

• Read and record stored freeze frame and pending counts; note conditions when code set
• Visually inspect fan assembly, wiring harness, connectors, junction boxes and relay/fuse locations for corrosion, damage or water ingress
• Check related fuses and relays for proper seating and operation
• Check battery voltage and charging system before tests (should be ~11–14.5 V with engine off/on as appropriate)
• Back-probe fan motor and control connector while commanding fan on/off with a diagnostic tool
• Measure resistance/continuity between control module pin and fan/relay pin, including grounds

Signal parameters

• Supply voltage to fan/relay feed: approximately 11–14.5 V (battery voltage range)
• Ground reference at fan/relay: near 0 V (low resistance to chassis ground)
• Control output (module to fan driver/relay): PWM or switched signal with variable duty cycle (0–100%) when commanded; frequency commonly in the tens to low hundreds of Hz — exact value varies by model
• Fan motor resistance (DC): typically low ohms (model dependent) — expect low single-digit ohms on a healthy motor
• Current draw when fan runs: significant (can be 5–40 A depending on fan); expect stable current without rapid dropouts
• Intermittent fault behavior: signal or voltage may drop to 0 V or float when fault occurs

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