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Home / DTC / P0691 — Fan 1 Control Circuit Low

P0691 — Fan 1 Control Circuit Low

Detailed page for trouble code P0691.

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23,014specific
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Code

P0691

Generic P — Powertrain

Fan 1 Control Circuit Low

Brand: Generic
Type: P — Powertrain
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Blown fuse for cooling fan circuit
  • Faulty fan relay or control module
  • Open or shorted wiring/connectors in fan control circuit
  • Failed fan motor
  • Poor ground connection
  • Faulty ECM/BCM output driver

Symptoms

  • Cooling fan does not run when engine is warm or when A/C is on
  • Engine runs hotter than normal, possible overheating
  • Reduced A/C cooling performance
  • Malfunction Indicator Lamp (MIL) illuminated
  • Cooling fan stuck off or intermittent operation

What to check

  • Scan for freeze-frame data and confirm P0691 is current or historic
  • Visual inspection: fuses, relay, wiring harness and connectors for damage/corrosion
  • Attempt to command Fan 1 ON with a scan tool while monitoring circuit
  • Backprobe fan connector and relay control pin to measure voltage when commanded
  • Apply 12V directly to fan motor to verify fan operation
  • Check continuity and resistance from fan relay output to fan and to ground

Signal parameters

  • Expected: control circuit shows a valid drive signal when commanded (either battery voltage or PWM).
  • Low (fault) condition: control circuit reads close to 0–0.5 V when fan should be driven.
  • High/ON: many systems show near battery voltage (≈11–14 V) or a PWM signal when commanded ON.
  • PWM frequency (if applicable): often in the range of ~20–300 Hz (varies by vehicle).
  • Fan motor typical resistance: usually a few ohms; excessive resistance or open indicates motor fault.

Diagnostic algorithm

  1. Verify the code with a scan tool. Note freeze-frame and whether the code is active or intermittent.
  2. Inspect fuses and relays related to the cooling fan circuit for proper seating and operation. Replace any suspect components.
  3. With ignition ON (engine cool) use the scan tool to command Fan 1 ON and observe whether the relay energizes and fan runs. If the relay clicks and fan runs, the circuit is likely OK.
  4. If fan does not run when commanded, backprobe the fan control wire at the relay and at the fan connector while commanding ON. Record voltages and compare with expected signal parameters.
  5. If control wire is low when commanded, isolate by checking continuity between relay/ECM and fan. Repair any open or shorted wires, secure grounds and connectors.
  6. Apply 12 V directly to the fan motor ground/power to verify motor operation. If fan runs with direct 12 V, the fan motor is likely good and problem is upstream (relay, wiring, or driver).
  7. If direct power does not run the fan, measure motor current and resistance. Replace the fan motor if out of spec or seized.
  8. If wiring, relay, and fan motor check good but control signal remains low, test or replace the ECM/BCM output driver per manufacturer procedures.
  9. After repairs, clear codes and perform a road/thermal test to confirm the fan engages under the required conditions and the code does not return.
  10. Safety: allow engine to cool before working near the fan and use insulated tools when probing live circuits.

Likely causes

  • Relay contacts failed and not supplying power to fan
  • Broken or high-resistance ground or power lead to fan motor
  • Connector pins corroded or pushed out at fan or relay
  • Fan motor seized or drawing excessive current causing protection to keep circuit low
  • Control driver in ECM has failed or is intermittently low

Fault status

⚠️ Status
ECM/BCM reports Fan 1 control circuit low — the control/switching circuit for cooling fan 1 is reading low voltage when the fan should be driven. Possible wiring fault, relay/fuse failure, fan motor issue, or control module output fault.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-2.5 hours

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Code

P0691

HUMMER P — Powertrain

Cooling Fan Relay Control Circuit Low Voltage

Brand: HUMMER
Type: P — Powertrain
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Blown fuse for cooling fan circuit
  • Faulty fan relay or control module
  • Open or shorted wiring/connectors in fan control circuit
  • Failed fan motor
  • Poor ground connection
  • Faulty ECM/BCM output driver

Symptoms

  • Cooling fan does not run when engine is warm or when A/C is on
  • Engine runs hotter than normal, possible overheating
  • Reduced A/C cooling performance
  • Malfunction Indicator Lamp (MIL) illuminated
  • Cooling fan stuck off or intermittent operation

What to check

  • Scan for freeze-frame data and confirm P0691 is current or historic
  • Visual inspection: fuses, relay, wiring harness and connectors for damage/corrosion
  • Attempt to command Fan 1 ON with a scan tool while monitoring circuit
  • Backprobe fan connector and relay control pin to measure voltage when commanded
  • Apply 12V directly to fan motor to verify fan operation
  • Check continuity and resistance from fan relay output to fan and to ground

Signal parameters

  • Expected: control circuit shows a valid drive signal when commanded (either battery voltage or PWM).
  • Low (fault) condition: control circuit reads close to 0–0.5 V when fan should be driven.
  • High/ON: many systems show near battery voltage (≈11–14 V) or a PWM signal when commanded ON.
  • PWM frequency (if applicable): often in the range of ~20–300 Hz (varies by vehicle).
  • Fan motor typical resistance: usually a few ohms; excessive resistance or open indicates motor fault.

Diagnostic algorithm

  1. Verify the code with a scan tool. Note freeze-frame and whether the code is active or intermittent.
  2. Inspect fuses and relays related to the cooling fan circuit for proper seating and operation. Replace any suspect components.
  3. With ignition ON (engine cool) use the scan tool to command Fan 1 ON and observe whether the relay energizes and fan runs. If the relay clicks and fan runs, the circuit is likely OK.
  4. If fan does not run when commanded, backprobe the fan control wire at the relay and at the fan connector while commanding ON. Record voltages and compare with expected signal parameters.
  5. If control wire is low when commanded, isolate by checking continuity between relay/ECM and fan. Repair any open or shorted wires, secure grounds and connectors.
  6. Apply 12 V directly to the fan motor ground/power to verify motor operation. If fan runs with direct 12 V, the fan motor is likely good and problem is upstream (relay, wiring, or driver).
  7. If direct power does not run the fan, measure motor current and resistance. Replace the fan motor if out of spec or seized.
  8. If wiring, relay, and fan motor check good but control signal remains low, test or replace the ECM/BCM output driver per manufacturer procedures.
  9. After repairs, clear codes and perform a road/thermal test to confirm the fan engages under the required conditions and the code does not return.
  10. Safety: allow engine to cool before working near the fan and use insulated tools when probing live circuits.

Likely causes

  • Relay contacts failed and not supplying power to fan
  • Broken or high-resistance ground or power lead to fan motor
  • Connector pins corroded or pushed out at fan or relay
  • Fan motor seized or drawing excessive current causing protection to keep circuit low
  • Control driver in ECM has failed or is intermittently low

Fault status

⚠️ Status
ECM/BCM reports Fan 1 control circuit low — the control/switching circuit for cooling fan 1 is reading low voltage when the fan should be driven. Possible wiring fault, relay/fuse failure, fan motor issue, or control module output fault.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-2.5 hours

Similar codes

P0690 P0692 P0480 P0481 P0482 P0483
Repair manuals

Manual library for HUMMER

138

Browse 138 HUMMER manuals: repair procedures, diagnostics, wiring diagrams, component locations, service data and Labor Times by year, model and trim.

HUMMER

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Code

P0691

LAND ROVER P — Powertrain

Fan 1 control - low circuit

Brand: LAND ROVER
Type: P — Powertrain
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Blown fuse for cooling fan circuit
  • Faulty fan relay or control module
  • Open or shorted wiring/connectors in fan control circuit
  • Failed fan motor
  • Poor ground connection
  • Faulty ECM/BCM output driver

Symptoms

  • Cooling fan does not run when engine is warm or when A/C is on
  • Engine runs hotter than normal, possible overheating
  • Reduced A/C cooling performance
  • Malfunction Indicator Lamp (MIL) illuminated
  • Cooling fan stuck off or intermittent operation

What to check

  • Scan for freeze-frame data and confirm P0691 is current or historic
  • Visual inspection: fuses, relay, wiring harness and connectors for damage/corrosion
  • Attempt to command Fan 1 ON with a scan tool while monitoring circuit
  • Backprobe fan connector and relay control pin to measure voltage when commanded
  • Apply 12V directly to fan motor to verify fan operation
  • Check continuity and resistance from fan relay output to fan and to ground

Signal parameters

  • Expected: control circuit shows a valid drive signal when commanded (either battery voltage or PWM).
  • Low (fault) condition: control circuit reads close to 0–0.5 V when fan should be driven.
  • High/ON: many systems show near battery voltage (≈11–14 V) or a PWM signal when commanded ON.
  • PWM frequency (if applicable): often in the range of ~20–300 Hz (varies by vehicle).
  • Fan motor typical resistance: usually a few ohms; excessive resistance or open indicates motor fault.

Diagnostic algorithm

  1. Verify the code with a scan tool. Note freeze-frame and whether the code is active or intermittent.
  2. Inspect fuses and relays related to the cooling fan circuit for proper seating and operation. Replace any suspect components.
  3. With ignition ON (engine cool) use the scan tool to command Fan 1 ON and observe whether the relay energizes and fan runs. If the relay clicks and fan runs, the circuit is likely OK.
  4. If fan does not run when commanded, backprobe the fan control wire at the relay and at the fan connector while commanding ON. Record voltages and compare with expected signal parameters.
  5. If control wire is low when commanded, isolate by checking continuity between relay/ECM and fan. Repair any open or shorted wires, secure grounds and connectors.
  6. Apply 12 V directly to the fan motor ground/power to verify motor operation. If fan runs with direct 12 V, the fan motor is likely good and problem is upstream (relay, wiring, or driver).
  7. If direct power does not run the fan, measure motor current and resistance. Replace the fan motor if out of spec or seized.
  8. If wiring, relay, and fan motor check good but control signal remains low, test or replace the ECM/BCM output driver per manufacturer procedures.
  9. After repairs, clear codes and perform a road/thermal test to confirm the fan engages under the required conditions and the code does not return.
  10. Safety: allow engine to cool before working near the fan and use insulated tools when probing live circuits.

Likely causes

  • Relay contacts failed and not supplying power to fan
  • Broken or high-resistance ground or power lead to fan motor
  • Connector pins corroded or pushed out at fan or relay
  • Fan motor seized or drawing excessive current causing protection to keep circuit low
  • Control driver in ECM has failed or is intermittently low

Fault status

⚠️ Status
ECM/BCM reports Fan 1 control circuit low — the control/switching circuit for cooling fan 1 is reading low voltage when the fan should be driven. Possible wiring fault, relay/fuse failure, fan motor issue, or control module output fault.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-2.5 hours

Similar codes

P0690 P0692 P0480 P0481 P0482 P0483
413

Browse 413 LAND ROVER manuals: repair procedures, diagnostics, wiring diagrams, component locations, service data and Labor Times by year, model and trim.

LAND ROVER

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Keep it short and practical. Up to 500 characters.
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