Damaged or chafed TCS signal wire shorted to a power source; Faulty TCS switch or sensor internal short; Corroded or loose electrical connector at the TCS module or ECM; Failed TCS control module or ABS module (integrated on many Subaru models); Poor ground connection for the TCS circuit causing reference voltage to float high; Water intrusion into the TCS harness or connector, leading to corrosion and high resistance; Rarely, a faulty ECM driver circuit for the TCS signal input

DTC codes / Subaru codes / P1124

P1124 · SubaruTCS Signal Circuit High Input

Q: What does code P1124 mean?

TCS Signal Circuit High Input. P1124 on a Subaru indicates that the Traction Control System (TCS) signal circuit is reporting an abnormally high voltage to the engine control module (ECM). The ECM monitors this circuit to coordinate engine torque reduction during traction control events, and a high input means the signal wire is seeing voltage above the expected range, often due to a short to power or an open ground.

P1124 on a Subaru indicates that the Traction Control System (TCS) signal circuit is reporting an abnormally high voltage to the engine control module (ECM). The ECM monitors this circuit to coordinate engine torque reduction during traction control events, and a high input means the signal wire is seeing voltage above the expected range, often due to a short to power or an open ground.

SystemPowertrain

Code typeSubaru specific

SeverityMedium

Fix difficultyIntermediate

AreaFuel and air metering

Symptoms you may notice

Traction control warning light illuminated on the dashboard
ABS warning light may also be on because the systems share components
Vehicle may default to reduced power or disable traction control entirely
Intermittent or no symptoms besides the warning light
Cruise control may become inoperative if the ECM limits torque control functions
Rough running or hesitation only if the fault affects throttle response during TCS activation

Common causes, most likely first

Damaged or chafed TCS signal wire shorted to a power source
Faulty TCS switch or sensor internal short
Corroded or loose electrical connector at the TCS module or ECM
Failed TCS control module or ABS module (integrated on many Subaru models)
Poor ground connection for the TCS circuit causing reference voltage to float high
Water intrusion into the TCS harness or connector, leading to corrosion and high resistance
Rarely, a faulty ECM driver circuit for the TCS signal input

How to diagnose and fix it

Connect a scan tool and record all stored codes and freeze-frame data to confirm P1124 is current and not history
Inspect the TCS-related wiring harness and connectors for visible damage, corrosion, or loose pins, especially near the ABS/TCS module and ECM
Measure reference voltage and ground continuity at the TCS signal circuit connector with a digital multimeter, comparing to factory specifications
Check for shorts to power by disconnecting both ends of the signal wire and testing resistance to battery positive
Test the TCS switch or sensor for internal short by measuring resistance across its terminals and comparing to the service manual
If wiring and components check out, substitute a known-good TCS module or ECM to isolate the fault
Clear codes and perform a road test to verify the repair, ensuring the TCS light stays off and no pending codes return

Subaru TCS Signal Circuit Quirks

On many Subaru models, the TCS signal is integrated into the ABS module, so a failing ABS module can set P1124 even when the ABS light is not on.
A weak battery or charging system issue can cause erratic TCS signals; always verify battery voltage and alternator output before condemning modules.
Aftermarket electrical accessories tapped into the TCS circuit, such as alarms or remote starters, are a common cause of high-voltage signals that set this code.
The TCS signal circuit often shares a ground with the throttle position sensor; a bad ground here can cause P1124 alongside driveability complaints.
P1124 can be set by a momentary voltage spike during jump-starting or battery replacement, so check if the code is history before extensive diagnostics.

Can I keep driving with P1124?

You can usually drive the vehicle with P1124 set, but traction control and ABS may be disabled, reducing safety in slippery conditions. Avoid aggressive acceleration or emergency maneuvers until the fault is repaired, and do not tow heavy loads if the vehicle enters limp mode.

Tools that help

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Guidance is general and written for Subaru vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.