What Does C1220 Mean?
The ABS module has detected that the ABS warning lamp output circuit is shorted to battery voltage. Instead of the ABS module controlling the lamp by providing a ground path, the circuit is seeing unwanted B+ voltage. This can cause the ABS warning lamp to behave erratically or remain off when it should be on. The ABS module may also be damaged by the external voltage on its output.
Common Causes
35%
Wiring harness damage where the ABS lamp circuit wire contacts a B+ power source due to chafed insulation
25%
Aftermarket alarm, remote start, or accessory wiring incorrectly tapped into the ABS lamp circuit introducing voltage
20%
Instrument cluster internal fault feeding voltage back onto the ABS lamp circuit
10%
Corroded or cross-connected pins in the ABS module or cluster connector allowing voltage bleed from an adjacent circuit
10%
ABS module internal failure with voltage present on the lamp driver output
Diagnostic Steps
1
Disconnect the ABS module connector. Using a DVOM, check for battery voltage on the ABS lamp output wire at the ABS module harness connector. Voltage present confirms an external short to B+ in the harness or cluster.
2
With the ABS module disconnected, also disconnect the instrument cluster connector. Re-check for voltage on the ABS lamp wire. If voltage is gone, the cluster is feeding voltage back; if still present, the short is in the harness.
3
Inspect the wiring between the ABS module and instrument cluster. Check for aftermarket wiring taps, damaged insulation near power distribution, or rodent damage.
4
Look for any aftermarket installations (alarm, remote start, LED conversions) that may have been connected to the ABS lamp circuit. Remove or properly isolate any unauthorized connections.
5
Repair the short, reconnect all connectors, clear codes, and verify proper ABS lamp operation during the key-on bulb check and while ABS faults are active.
Estimated Repair Cost
$50 - $500
Parts + labor, varies by vehicle and location
The ABS module has detected that the ABS warning lamp output circuit is shorted to battery voltage. Instead of the ABS module controlling the lamp by providing a ground path, the circuit is seeing unwanted B+ voltage. This can cause the ABS warning lamp to behave erratically or remain off when it sh...
The most common cause of C1220 (Lamp ABS Warning Output Circuit Short To Battery) is: Wiring harness damage where the ABS lamp circuit wire contacts a B+ power source due to chafed insulation
Typical repair costs for C1220 range from $50 to $500, depending on the vehicle, location, and whether you do it yourself or go to a shop.
The ABS warning lamp may not function correctly, meaning the driver might not be alerted to genuine ABS faults. Additionally, backfeeding voltage into the ABS module's lamp driver output could potentially damage the module over time. Repair promptly to ensure the warning system works as designed.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to C1220 to identify the root cause.
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Quick Info
Category
Chassis
System
ABS / Traction Control
Difficulty
Type
Manufacturer
Recommended Tools
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