Code
P1666
GM
P — Powertrain
Driver 3 Line 6
AI status
Completed
Completed
100%
Causes
- Open circuit in the driver output wiring (broken wire, disconnected terminal)
- Short to battery (voltage) or short to ground in the driver circuit
- Corroded or loose connector at the controlled component or PCM
- Failed controlled device (actuator, solenoid, injector, relay coil)
- Failed PCM/ECM output transistor or internal driver
- Water intrusion or physical damage to harness near connector
Symptoms
- Malfunction indicator lamp (MIL) illuminated
- Associated component may not operate or operates intermittently
- Related system performance issues (engine drivability, emissions, accessory function) depending on the controlled device
- Possible reduced engine power or limp-in mode if critical circuit is affected
- Stored freeze-frame and data PIDs related to the event
What to check
- Read freeze frame and live data with a scan tool; record state of related PIDs when code set
- Identify which component the driver controls using factory wiring diagrams
- Visually inspect connectors and wiring for damage, corrosion, or foreign material
- Backprobe connector and measure voltage with key ON / engine OFF and while commanding the output with a scan tool
- Check for continuity and resistance between PCM pin and component connector, and to ground as appropriate
- Perform wiggle test on wiring while monitoring circuit voltage/scan data
Signal parameters
- Low-side (ground-switching) driver: approximately battery voltage (~11–14.5 V) at component when driver OFF; ~0 V at component when driver ON
- High-side driver: ~0 V at component when OFF; ~battery voltage (~11–14.5 V) when ON
- Pulse-width modulated outputs may toggle between 0 V and battery voltage; frequency varies by function (typical range: 1 Hz to several hundred Hz)
- Static continuity: typical coil/actuator resistance ranges from a few ohms (motor/coil) to hundreds of ohms (some solenoids); consult factory spec for exact value
- Current draw: watch for excessive current (short) or zero/very low current (open)
Diagnostic algorithm
- Use a scanner to read code, freeze frame, and live PIDs. Note vehicle state when code set (temp, rpm, load).
- Consult factory service information to identify exact PCM pin and the controlled component for "Driver 3 Line 6."
- Visually inspect the wiring harness and connectors at the PCM and the controlled device for damage, corrosion, or water intrusion.
- With key ON (engine OFF), measure voltage at the component connector power and ground terminals. Compare to battery voltage.
- Command the output ON/OFF with the scan tool while monitoring voltage at the component. Observe behavior and listen for actuator operation.
- If output does not command correctly, test continuity and resistance from PCM pin to component connector; repair any open or high-resistance wiring.
- Check for short to battery or ground: disconnect the load and measure for shorts on the harness side. Repair any shorted wiring.
- If wiring and load test good, test or substitute the controlled device (if possible) to rule out a faulty actuator.
- If load and wiring confirm good, follow factory procedures to test the PCM driver (bench/oscilloscope tests or module replacement guidelines). Do not replace the PCM without confirming driver fault.
- After repairs, clear codes and road-test. Re-scan to ensure code does not return and monitor related parameters.
Likely causes
- Open or intermittent wiring between PCM and controlled device
- Corroded/poor connector or pin(s) at load or PCM
- Failed actuator/solenoid drawing abnormal current
- Short to ground or short to battery on the driver circuit
- Internal PCM driver failure (less common after wiring checked)
Fault status
Status
GM-specific code for a fault detected on output 'Driver 3 Line 6' — indicates abnormal circuit condition (open/short/driver fault) between PCM and controlled device.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
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