Code
C1738
HUMMER
C — Chassis
Exhaust Solenoid Valve Short to GND
AI status
Completed
Completed
100%
Causes
- Damaged or chafed wiring harness causing a conductor to contact chassis ground
- Corroded, loose, or water-intruded connector at the exhaust solenoid
- Internal short in the exhaust solenoid coil
- Incorrect aftermarket replacement part or incorrect installation
- Poor or missing power/diagnostic ground at connector
- Faulty engine/control module (rare) or internal driver transistor failure
Symptoms
- Service/Check Engine light or chassis/system warning lamp illuminated
- Exhaust-related control features not operating (e.g., exhaust bypass, turbo valve, or emissions control) depending on vehicle
- Reduced engine performance, increased noise, or altered exhaust tone when solenoid fails to operate
- Possible increased emissions or limp mode if the system protects itself
- Stored fault code(s) and the system may disable related functions
What to check
- Read all stored DTCs and freeze frame data with a capable scan tool; note related codes
- Visually inspect the exhaust solenoid, connector, and wiring for damage, corrosion, or water
- Backprobe the solenoid connector with key ON and command the solenoid ON/OFF using a scan tool to observe voltages
- Measure solenoid coil resistance with the connector disconnected and compare to spec (see factory manual)
- Perform a continuity/short-to-ground check between the solenoid control pin and chassis ground
- Wiggle test the harness while monitoring voltage or resistance to reproduce an intermittent short
Signal parameters
- Nominal coil resistance (typical): consult factory spec; many solenoids are roughly 10–50 ohms (check service manual)
- Short-to-ground symptom: near 0 ohms between control pin and chassis ground or
- Open symptom: infinite or very high resistance when solenoid disconnected
- Commanded voltage: when commanded ON the control module either supplies battery voltage or switches to ground — verify expected behavior in service data
- Current draw when energized: typical solenoid currents often range 0.1–1.0 A; significantly higher current indicates a shorted coil
Diagnostic algorithm
- Verify the code and note any additional DTCs. Record freeze frame data and the state when the fault set.
- Visual inspection: examine the solenoid, connector, and entire harness routing for signs of damage, rubbing, heat, or contamination. Repair visible damage.
- Disconnect the solenoid connector. Measure coil resistance across the solenoid terminals. If resistance is near 0 ohms or out of spec, replace the solenoid.
- With the solenoid disconnected, check for continuity between the control circuit pin and chassis ground. If there is continuity (short to ground), trace harness for damage or disconnect at splice points to isolate the short.
- Backprobe the connector with key ON and command the solenoid using a scan tool to observe whether the module applies voltage or ground. Verify switching behavior matches factory procedure.
- If wiring is open or shorted, repair the damaged section (splice, replace harness, or repair connector). Protect and secure harness away from heat or moving parts.
- After repair or replacement, clear codes and perform a functional test and road test to confirm repair and that the DTC does not return.
- If wiring and the solenoid check good but code returns, suspect the control module driver. Before replacing the module, consult manufacturer service information for module bench tests or reprogramming procedures.
Likely causes
- Pinched or rubbed wiring near exhaust components or suspension
- Connector pins corroded or bent at solenoid plug
- Solenoid coil shorted internally due to heat or contamination
- Repair or service work left connector damaged or misrouted
- Short to ground in a splice or harness junction
Fault status
Status
C1738 — Exhaust Solenoid Valve Circuit Short to Ground: control module detected a short between the solenoid control circuit and chassis ground. Possible wiring, connector, or solenoid fault. Diagnostic inspection recommended.
Repair difficulty: Medium
Diagnostic time: 0.5-2.5 hours
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Repair manuals
Manual library for HUMMER
138
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