Code
P1660
HUMMER
P — Powertrain
Cooling Fan Control Circuits
Views:
UK: 17
EN: 30
RU: 28
AI status
Completed
Completed
100%
Causes
- Open or shorted wiring in cooling fan supply or control circuit
- Corroded or disconnected connector at fan motor, relay, or ECM
- Failed cooling fan motor
- Faulty fan relay or fuse
- Faulty ECM / fan control module
- Intermittent connection or water intrusion in harness
Symptoms
- Cooling fan(s) do not turn on when commanded
- Cooling fan(s) run continuously or at incorrect speed
- Engine runs hotter than normal or overheats
- Reduced A/C cooling performance
- Malfunction Indicator Lamp (MIL) illuminated
- Intermittent fan operation or code stored intermittently
What to check
- Verify DTC P1660 and note freeze frame / conditions using a scan tool
- Visually inspect fan, relay, fuse, wiring harnesses and connectors for damage or corrosion
- Check for related DTCs (coolant temp sensor, fan relays, BCM/PCM communication)
- Measure voltage at fan power and control terminals with fan commanded on and off
- Check continuity to ground and resistance of fan motor
- Backprobe relay socket to confirm relay coil control and supply
Signal parameters
- Control type: switched 12V or ground side drive controlled by ECM or fan control module; some models use PWM
- Expected voltage: approximately battery voltage (12–14V) at power feed; control line 0V (ground) or battery voltage when commanded depending on design
- Off condition: control line typically open/high-impedance or opposite logic; voltage near battery or 0V depending on circuit type
- On condition (steady): supply or control line shows battery voltage or ground path established
- PWM control: duty cycle 0–100%; typical PWM frequency commonly in the low hundreds of Hz (varies by model)
- Fan motor current draw: typically several amps (small fans) up to 20–30 A for high-load fans; compare to factory spec
Diagnostic algorithm
- Read and record the DTC with a capable scan tool. Note freeze-frame data and any related codes.
- Visually inspect fuses, fan relay(s), relay socket, fan motor connector, and wiring for corrosion, damage, or loose pins.
- With ignition on (engine off), check fuse continuity and apply battery voltage to fan motor power terminal (while securely supported) to confirm motor operation. If fan does not run or runs weakly, replace motor.
- Command the fan ON using a scan tool while monitoring voltage at the fan power and control pins. If ECM commands the fan but there is no voltage change at the fan connector, isolate between relay and fan.
- If relay is used, verify relay coil is being energized when commanded. Backprobe relay control and supply terminals; swap relay with known good of same type if available.
- Measure resistance and continuity of the control circuit from ECM/fan control module to fan relay or motor. Repair any opens or shorts.
- Check ground integrity for the fan motor and control module. Clean and secure grounds as needed.
- If control line shows abnormal PWM or voltage that does not match expected behavior, test/replace the fan control module or ECM output driver per factory procedure.
- After repairs, clear codes and perform functional test and road/test to confirm the fan operates correctly under load and the code does not return.
- Safety note: when applying power to fan or probing live circuits, secure fan shroud and avoid loose clothing or tools near spinning fan blades. Disconnect battery before performing major wiring repairs.
Likely causes
- Blown fuse or bad fan relay
- Fan motor seized or drawing excessive current
- Corroded connector or broken wire at fan motor
- Short to ground on the control wire or open ground
- ECM output driver fault (less common)
Fault status
Status
ECM detected malfunction in cooling fan control circuit — fan not responding or abnormal electrical condition in fan control.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
Similar codes
HTML Workshop Manuals AI manual library for HUMMER Click to show available manuals 77
HUMMER 2010 H3 Alpha
HTML ManualHUMMER 2010 H3 Base, Standard
HTML ManualHUMMER 2010 H3 Base, Automatic
HTML ManualHUMMER 2010 H3T Alpha
HTML ManualHUMMER 2010 H3T Base, Standard
HTML ManualHUMMER 2010 H3T Base, Automatic
HTML ManualHUMMER 2009 H2 4D Utility Wagon
HTML ManualHUMMER 2009 H2 4D Utility Pickup
HTML ManualYour experience will help others
+100 karma for a short comment :)
Was this AI description helpful?
Your feedback helps improve AI descriptions.
👍 Like
0
👎 Dislike
0
Send to email