What Does C1123 Mean?
This code indicates the vehicle's chassis control module detected a voltage on the vehicle speed sensor (VSS) signal circuit that is higher than expected, specifically showing a short to battery voltage (typically 12-14V). The VSS provides critical wheel speed or transmission output shaft speed data to multiple vehicle systems including ABS, traction control, speedometer, cruise control, and transmission shift logic. This electrical fault prevents the module from receiving accurate speed data, compromising safety and driveability systems.
Safety Warning
This is a critical safety concern as ABS, traction control, stability control, and speedometer will be inoperative or providing false data. Vehicle should not be driven except to a repair facility as braking performance and accident avoidance systems are compromised.
Common Causes
45%
Damaged or chafed wiring harness causing the VSS signal wire to contact a power wire or circuit
30%
Failed vehicle speed sensor with internal short circuit to power supply
15%
Corrosion or moisture intrusion in VSS connector causing cross-circuit contamination
10%
Fault within the chassis control module or ABS module causing improper voltage reference
Diagnostic Steps
1
Step 1: Perform thorough visual inspection of all vehicle speed sensor wiring from sensor to module, checking for pinched, chafed, or damaged wires especially near moving components, exhaust, and body pinch points
2
Step 2: Disconnect the vehicle speed sensor connector and measure voltage on the signal wire at the harness side with ignition on - reading should be 0-0.5V; if 12V+ is present, wiring harness has short to power between sensor and module
3
Step 3: With sensor disconnected, use multimeter to check resistance between VSS signal wire and ground, then signal wire and battery positive - infinite resistance indicates no short; low resistance (under 10k ohms) confirms short location
4
Step 4: If wiring tests normal, measure resistance across VSS terminals per manufacturer specifications (typically 800-1400 ohms for magnetic sensors) - out-of-spec readings indicate sensor failure
5
Step 5: Inspect VSS connector for bent pins, corrosion, or moisture; clean with electrical contact cleaner and ensure proper pin tension and seal integrity
6
Step 6: After repairs, clear codes, road test vehicle at various speeds while monitoring live VSS data to confirm proper signal voltage range (typically 0-5V AC or square wave) and verify code does not return
Estimated Repair Cost
$150 - $650
Parts + labor, varies by vehicle and location
This code indicates the vehicle's chassis control module detected a voltage on the vehicle speed sensor (VSS) signal circuit that is higher than expected, specifically showing a short to battery voltage (typically 12-14V). The VSS provides critical wheel speed or transmission output shaft speed data...
The most common cause of C1123 (Vehicle Speed Sensor Input Short to Battery) is: Damaged or chafed wiring harness causing the VSS signal wire to contact a power wire or circuit
Typical repair costs for C1123 range from $150 to $650, depending on the vehicle, location, and whether you do it yourself or go to a shop.
This is a critical safety concern as ABS, traction control, stability control, and speedometer will be inoperative or providing false data. Vehicle should not be driven except to a repair facility as braking performance and accident avoidance systems are compromised.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to C1123 to identify the root cause.
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Quick Info
Category
Chassis
System
Chassis Control / ABS / Vehicle Speed Sensing
Difficulty
Type
Manufacturer
Recommended Tools
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