C1220
Lamp ABS Warning Output Circuit Short To Battery
Chassis Chassis/Safety ABS Lamp Circuit 🔴 Serious — Stop or limit driving
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What This Actually Means
In plain language — no jargon

The ABS warning lamp circuit is shorted directly to battery power, meaning the lamp stays on constantly instead of turning on/off as needed. It's like a light switch that's permanently stuck in the ON position due to a wiring problem.

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Symptoms You May Notice
3 known symptoms for this code
ABS warning lamp illuminated continuously on dashboard
ABS system may be disabled or in limp mode
Possible loss of anti-lock braking function
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Embedded Systems Insight
What the ECU/ECM is actually computing

The ECU monitors the voltage on the ABS warning lamp output circuit, expecting it to toggle between ground (lamp ON) and high voltage (lamp OFF). When the circuit is shorted to battery voltage, the ECU detects constant high voltage instead of the expected control signal, indicating an electrical fault in the lamp driver circuit or wiring.

Voltage & Parameter Thresholds

Parameter Normal Range Fault Condition
Lamp Output Voltage 0V (ON) to 12V (OFF) switching Constant 12V+ detected
Circuit Resistance 20-100 ohms when activated Open or shorted to battery
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Diagnostic & DIY Fix Guide
Check these in order — from cheapest to most complex
1
ABS warning lamp connector
Inspect and reseat the connector at the lamp assembly to eliminate poor contact causing false short.
2
Wiring harness (ABS lamp circuit)
Check for damaged or pinched wires between the ABS module and instrument cluster; repair or replace compromised sections.
3
ABS module output driver
If wiring is intact, the ABS control module lamp driver circuit may be internally shorted and require module replacement.