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Home / DTC / C1721 — Left Rear Damper Actuator Short Circuit to Ground

C1721 — Left Rear Damper Actuator Short Circuit to Ground

Detailed page for trouble code C1721.

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Code

C1721

HUMMER C — Chassis

Left Rear Damper Actuator Short Circuit to Ground

Brand: HUMMER
Type: C — Chassis
Views: UK: 9 EN: 9 RU: 13
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Damaged or pinched wiring harness between suspension control module and left rear damper actuator causing insulation breach and contact with chassis ground
  • Corroded, bent or pushed-out connector pins at the damper actuator or module connector
  • Internal short inside the left rear damper actuator (winding or internal electronics)
  • Water intrusion or contamination in the connector or actuator causing short to ground
  • Faulty suspension control module output transistor or driver stage
  • Aftermarket work or collision damage that disturbed the harness

Symptoms

  • Suspension fault warning or suspension service lamp on dash
  • Reduced or no variable damping at left rear corner (stiffer or uncontrolled ride)
  • Uneven ride height or handling complaints on one side
  • Diagnostic Trouble Code C1721 stored in suspension control module
  • Possible limp-home or default suspension mode engaged

What to check

  • Read and record all suspension-related codes and freeze-frame data with a scan tool that supports the vehicle
  • Visual inspection of left rear damper actuator connector and wiring for damage, corrosion, pin push-out, or water ingress
  • Inspect harness routing at wheelwell, axle, and frame for chafe points or recent repair areas
  • Verify fuse(s) and relays for the suspension/damper system are intact and correct
  • With ignition ON (engine off) backprobe and measure control circuit voltage; check for near 0V indicating shorted-to-ground
  • With ignition OFF perform resistance-to-ground checks on actuator control wires (connector disconnected) — should be open/very high resistance

Signal parameters

  • Expected control signal: switched/PWM output from suspension module (0–battery voltage depending on duty cycle)
  • With actuator connected and command active: variable duty-cycle PWM; voltage should not sit at 0V continuously
  • Actuator static DC resistance: typically low (actuator coils/driver electronics) — should NOT show direct continuity to chassis ground with connector disconnected
  • With connector disconnected: continuity between control pin and chassis ground should read open (no continuity or very high ohms)
  • Supply/battery voltage present at system power pin with ignition ON: ~12V

Diagnostic algorithm

  1. Retrieve and record codes and suspension module data. Note whether the code is current or historical and any related codes.
  2. Perform a careful visual inspection of the left rear damper actuator, connector and wiring route. Look for chafe, pin corrosion, broken wires, or evidence of water intrusion.
  3. Confirm power and ground to the suspension system (fuses/relays); verify battery voltage at the module power feed with ignition ON.
  4. With ignition OFF, disconnect the left rear damper actuator connector. Measure resistance/continuity between the actuator control pin(s) and chassis ground. A low resistance indicates a short to ground in wiring or actuator.
  5. If low resistance to ground is present at the disconnected connector, isolate by opening the harness along the route and testing sections or disconnecting other intermediate connectors until the short location is found. Repair damaged wiring or replace connector as required.
  6. If no short is present at the actuator connector, reconnect and backprobe the control wire with ignition ON. Command the module to activate the damper while observing voltage. If the module output reads near 0V while commanding (and wiring to actuator is good), suspect internal module driver failure.
  7. If available, use a scope to verify PWM parameters and check for noise or abnormal waveform that indicates driver stress or shorting.
  8. If actuator wiring and connector test good but the actuator shows internal short characteristics, remove and bench-test or replace the actuator.
  9. After repair or replacement, clear codes and perform a road test with the scan tool to confirm proper damper control and that C1721 does not return.
  10. If replacement of the suspension control module is required, confirm all wiring is repaired and perform any required module programming or calibration per factory procedures.

Likely causes

  • Wiring harness chafe or rubbing through to chassis at left rear wheelwell or mounting points
  • Corroded/contaminated actuator connector at wheel or module connector underbody
  • Failed actuator with internal short
  • Failed suspension/ride control module output driver

Fault status

⚠️ Status
Left rear damper actuator circuit fault: short to ground detected. Suspension control module unable to drive left rear damper properly.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-2.5 hours

Similar codes

C1720 C1711 C1710 C1731 U0415
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Code

C1721

Other C — Chassis

Air Suspension Height Sensor Power Circuit Open

Brand: Other
Type: C — Chassis
Views: UK: 15 EN: 30 RU: 22
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Damaged or pinched wiring harness between suspension control module and left rear damper actuator causing insulation breach and contact with chassis ground
  • Corroded, bent or pushed-out connector pins at the damper actuator or module connector
  • Internal short inside the left rear damper actuator (winding or internal electronics)
  • Water intrusion or contamination in the connector or actuator causing short to ground
  • Faulty suspension control module output transistor or driver stage
  • Aftermarket work or collision damage that disturbed the harness

Symptoms

  • Suspension fault warning or suspension service lamp on dash
  • Reduced or no variable damping at left rear corner (stiffer or uncontrolled ride)
  • Uneven ride height or handling complaints on one side
  • Diagnostic Trouble Code C1721 stored in suspension control module
  • Possible limp-home or default suspension mode engaged

What to check

  • Read and record all suspension-related codes and freeze-frame data with a scan tool that supports the vehicle
  • Visual inspection of left rear damper actuator connector and wiring for damage, corrosion, pin push-out, or water ingress
  • Inspect harness routing at wheelwell, axle, and frame for chafe points or recent repair areas
  • Verify fuse(s) and relays for the suspension/damper system are intact and correct
  • With ignition ON (engine off) backprobe and measure control circuit voltage; check for near 0V indicating shorted-to-ground
  • With ignition OFF perform resistance-to-ground checks on actuator control wires (connector disconnected) — should be open/very high resistance

Signal parameters

  • Expected control signal: switched/PWM output from suspension module (0–battery voltage depending on duty cycle)
  • With actuator connected and command active: variable duty-cycle PWM; voltage should not sit at 0V continuously
  • Actuator static DC resistance: typically low (actuator coils/driver electronics) — should NOT show direct continuity to chassis ground with connector disconnected
  • With connector disconnected: continuity between control pin and chassis ground should read open (no continuity or very high ohms)
  • Supply/battery voltage present at system power pin with ignition ON: ~12V

Diagnostic algorithm

  1. Retrieve and record codes and suspension module data. Note whether the code is current or historical and any related codes.
  2. Perform a careful visual inspection of the left rear damper actuator, connector and wiring route. Look for chafe, pin corrosion, broken wires, or evidence of water intrusion.
  3. Confirm power and ground to the suspension system (fuses/relays); verify battery voltage at the module power feed with ignition ON.
  4. With ignition OFF, disconnect the left rear damper actuator connector. Measure resistance/continuity between the actuator control pin(s) and chassis ground. A low resistance indicates a short to ground in wiring or actuator.
  5. If low resistance to ground is present at the disconnected connector, isolate by opening the harness along the route and testing sections or disconnecting other intermediate connectors until the short location is found. Repair damaged wiring or replace connector as required.
  6. If no short is present at the actuator connector, reconnect and backprobe the control wire with ignition ON. Command the module to activate the damper while observing voltage. If the module output reads near 0V while commanding (and wiring to actuator is good), suspect internal module driver failure.
  7. If available, use a scope to verify PWM parameters and check for noise or abnormal waveform that indicates driver stress or shorting.
  8. If actuator wiring and connector test good but the actuator shows internal short characteristics, remove and bench-test or replace the actuator.
  9. After repair or replacement, clear codes and perform a road test with the scan tool to confirm proper damper control and that C1721 does not return.
  10. If replacement of the suspension control module is required, confirm all wiring is repaired and perform any required module programming or calibration per factory procedures.

Likely causes

  • Wiring harness chafe or rubbing through to chassis at left rear wheelwell or mounting points
  • Corroded/contaminated actuator connector at wheel or module connector underbody
  • Failed actuator with internal short
  • Failed suspension/ride control module output driver

Fault status

⚠️ Status
Left rear damper actuator circuit fault: short to ground detected. Suspension control module unable to drive left rear damper properly.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-2.5 hours

Similar codes

C1720 C1711 C1710 C1731 U0415
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