What Does P1678 Mean?
The Malfunction Indicator Lamp (MIL) control circuit for the electronic throttle control (drive-by-wire) system has detected a short to ground. This prevents proper MIL illumination for throttle-related faults.
Common Causes
35%
Damaged wiring harness between ECM and instrument cluster with chafed insulation causing ground short
25%
Failed ECM internal MIL driver circuit shorted to ground
20%
Corroded or damaged instrument cluster connector with moisture intrusion
15%
Short circuit in instrument cluster MIL bulb socket or LED circuit
5%
Aftermarket alarm or accessory installation causing wiring damage
Diagnostic Steps
1
Step 1: Inspect wiring harness between ECM and instrument cluster for visible damage, chafing, or pinch points
2
Step 2: Disconnect instrument cluster and measure resistance between MIL control wire and ground (should be >10k ohms)
3
Step 3: Check ECM connector pins for corrosion, bent pins, or moisture and verify connector integrity
4
Step 4: Perform voltage drop test on MIL control circuit with key on to locate short location
5
Step 5: If wiring is intact, test ECM MIL driver output with oscilloscope or substitute known-good ECM
Estimated Repair Cost
$150 - $800
Parts + labor, varies by vehicle and location
The Malfunction Indicator Lamp (MIL) control circuit for the electronic throttle control (drive-by-wire) system has detected a short to ground. This prevents proper MIL illumination for throttle-related faults.
The most common cause of P1678 (Drive By Wire MIL Circuit Short To Ground) is: Damaged wiring harness between ECM and instrument cluster with chafed insulation causing ground short
Typical repair costs for P1678 range from $150 to $800, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Vehicle remains drivable but MIL may not illuminate for critical throttle system faults, potentially masking serious issues.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P1678 to identify the root cause.
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Quick Info
Category
Powertrain
System
Electronic Throttle Control / MIL Circuit
Difficulty
Type
Manufacturer
Recommended Tools
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