C0139 is a chassis-related diagnostic trouble code that, on applicable GM vehicles, means Base Brake System Pressure Circuit/Sensor High. The Electronic Brake Control Module (EBCM) monitors brake-fluid pressure through pressure-sensor inputs used for ABS and vehicle stability functions. A C0139 code can indicate an abnormally high pressure-sensor signal or a related circuit problem.
C0139 may be encountered on applicable Chevrolet, Buick, Cadillac, GMC, Pontiac, and other GM vehicles. The exact brake-pressure sensor design, wiring arrangement, hydraulic module configuration, and diagnostic procedure depend on the specific vehicle and model year.
Fault Code Description
C0139 = Base Brake System Pressure Circuit/Sensor High.
Code type: Chassis / ABS-related Diagnostic Trouble Code.
Likely fault location: Brake pressure sensor circuit, pressure sensor, EBCM wiring, 5-volt reference circuit, low-reference circuit, connector, or the electronic brake control/hydraulic module.
The word High indicates that the EBCM is detecting a brake-pressure signal that is higher than the expected operating range or inconsistent with the vehicle's operating conditions. It does not automatically mean that the hydraulic pressure itself is physically too high.
What Does C0139 Mean?
The EBCM uses brake-fluid pressure sensor information to determine how much braking force the driver is requesting and to assist ABS, traction control, and vehicle stability functions. On applicable GM systems, C0139 can be set when the brake-pressure signal remains unusually high under conditions where the module expects the signal to change appropriately.
For example, GM service information describes C0139 as a condition in which the vehicle is accelerating above a specified speed while the brake-pressure signal remains high. On some applications, the pressure signal is expected to be below approximately 150 psi during the relevant operating condition. Exact thresholds vary by application. 0
Symptoms of C0139
- ABS warning light.
- Service Stability System message.
- Traction Control warning light.
- ABS or stability-control functions may be disabled.
- Brake-system warning indicators.
- Abnormal brake-pressure data in scan-tool live data.
- Additional ABS or brake-system codes.
- In some applications, normal basic braking may remain available.
On some GM applications, setting C0139 can cause the EBCM to disable traction control and vehicle stability enhancement functions for the ignition cycle, while ABS operation may remain available. 1
Common Causes of C0139
- Faulty brake-fluid pressure sensor.
- Abnormally high pressure-sensor signal.
- Short to voltage in the pressure-sensor signal circuit.
- Damaged or corroded wiring.
- Poor electrical connection at the EBCM.
- Damaged connector terminals.
- Fault in the 5-volt reference circuit.
- Fault in the low-reference circuit.
- Internal hydraulic control-module problem.
- Electronic Brake Control Module (EBCM) fault.
On some GM applications, the brake-pressure sensor is integrated into the brake pressure modulator valve (BPMV) beneath the EBCM and may not be serviced as a separate component. 2
How to Fix C0139
1. Scan the ABS System
Use a professional scan tool capable of communicating with the EBCM/ABS module. A basic engine-only OBD-II scanner may not provide the pressure-sensor data or ABS-specific diagnostic information required for C0139.
2. Check All Related Codes
Record all stored and current ABS, brake-pressure, traction-control, and stability-control codes before clearing them. Related codes can help determine whether the problem is isolated to the pressure circuit or is caused by a shared reference or ground circuit.
3. Inspect the Brake Pressure Circuit
Inspect the EBCM connector, pressure-sensor circuit, wiring, terminals, and grounds for corrosion, loose connections, damaged insulation, water intrusion, or previous wiring repairs.
4. Check the 5-Volt Reference
Use the vehicle-specific wiring diagram and manufacturer's specifications to verify the pressure sensor's 5-volt reference circuit. A reference-voltage problem can affect pressure-sensor readings and may generate additional DTCs.
5. Check the Pressure Sensor Signal
Monitor the brake-pressure sensor signal with the scan tool while applying and releasing the brake pedal. The pressure reading should respond appropriately to pedal application and release.
6. Compare Pressure Data With Brake Operation
If the scan tool shows high brake pressure while the brake pedal is released and the vehicle is operating normally, investigate the sensor signal, wiring, reference circuit, and hydraulic module.
7. Test the EBCM/BPMV
If the sensor circuit, wiring, reference voltage, and connectors test correctly, follow the manufacturer's diagnostic procedure for the EBCM and brake pressure modulator valve before considering module replacement.
C0139 Diagnostic Signal Flow
↓
Master Cylinder / Hydraulic Brake Pressure
↓
Brake Pressure Sensor
↓
Sensor Signal Circuit
↓
EBCM / ABS Module
↓
ABS / Traction Control / Stability Control
C0139 OBD Live Data
Use an ABS-capable scan tool to monitor available brake pressure sensor data, brake-pedal status, vehicle speed, ABS status, traction-control status, and stability-control parameters.
The pressure reading should change logically when the brake pedal is applied and released. A pressure value that remains excessively high when the pedal is released can help direct the diagnosis toward the pressure sensor, signal circuit, reference circuit, or EBCM.
Live data should be combined with electrical testing because a wiring or connector fault may produce an intermittent or misleading pressure reading.
C0139 Chevrolet, Buick, Cadillac and GMC
C0139 Chevrolet
On applicable Chevrolet vehicles, C0139 refers to a high condition in the base brake system pressure circuit/sensor. Check the EBCM, pressure-sensor circuit, connectors, wiring, and related reference circuits before replacing the hydraulic module.
C0139 Buick
On applicable Buick vehicles, the EBCM uses brake-pressure sensor information for ABS and stability functions. Diagnosis should focus on the pressure signal, wiring, reference circuit, and EBCM/BPMV assembly.
C0139 Cadillac
On applicable Cadillac vehicles, C0139 can affect stability and traction-control functions. The pressure sensor and EBCM circuit should be tested using the vehicle-specific diagnostic procedure.
C0139 GMC
On applicable GMC vehicles, inspect the brake pressure sensor circuit, EBCM connector, wiring, reference voltage, and hydraulic control assembly when diagnosing C0139.
The examples above do not mean that every Chevrolet, Buick, Cadillac, or GMC vehicle uses an identical C0139 circuit. The exact pressure-sensor arrangement and diagnostic thresholds depend on the vehicle and model year.
Is C0139 Serious?
C0139 can be serious because it is related to the brake-pressure monitoring system and may disable traction-control or stability-control functions. On some applications, the basic hydraulic brakes and ABS may remain functional, but the vehicle should still be diagnosed promptly.
If the brake pedal feels abnormal, braking performance changes, a brake-fluid leak is present, or multiple brake-system warning lights appear, the vehicle should be inspected before continued driving.
Can I Drive With C0139?
Limited driving may be possible on some vehicles if normal braking remains unaffected, but C0139 should not be ignored. Depending on the vehicle, traction control and stability-control functions may be disabled while the fault is active.
Avoid driving if the brake pedal becomes soft or hard unexpectedly, braking performance is reduced, brake fluid is leaking, or the vehicle behaves abnormally during braking.
C0139 Repair Cost
- ABS diagnostic scan: approximately $50–$150+.
- Electrical diagnosis or wiring repair: approximately $80–$300+.
- Connector repair: approximately $80–$200+.
- Brake pressure sensor or related component: approximately $150–$500+ where separately serviceable.
- ABS hydraulic module/BPMV: approximately $500–$1,500+.
- EBCM replacement or programming: approximately $500–$1,500+ depending on the vehicle.
These are general estimates only. Actual repair costs depend on the vehicle, brake-system design, parts availability, programming requirements, and labor rate.
Common Repair Mistakes
- Replacing the EBCM without testing the pressure circuit.
- Assuming the pressure sensor itself is defective.
- Ignoring the 5-volt reference circuit.
- Failing to inspect EBCM connectors and terminals.
- Using an engine-only scanner instead of an ABS-capable scan tool.
- Ignoring additional ABS codes.
- Replacing the hydraulic module without checking wiring.
- Failing to compare live brake-pressure data with actual brake-pedal operation.
Related Codes
- C0131 – Antilock Brake System (ABS) Pressure Circuit.
- C0136 – Base Brake System Pressure Circuit/Sensor.
- C0138 – Base Brake System Pressure Circuit/Sensor Low.
- C0139 – Base Brake System Pressure Circuit/Sensor High.
- C0870 – 5-Volt Reference-related fault on applicable GM systems.
C0131, C0136, C0138, and C0139 are part of the GM brake-pressure diagnostic group on applicable systems. The exact relationship and diagnostic procedure depend on the vehicle. 3
FAQ About C0139
What does C0139 mean?
On applicable GM vehicles, C0139 means Base Brake System Pressure Circuit/Sensor High. The EBCM has detected an abnormally high brake-pressure sensor signal or an associated circuit condition.
Is C0139 an engine code?
No. C0139 is a chassis and brake/ABS-related code, not a conventional engine powertrain P-code.
Is C0139 a generic OBD-II code?
C0139 is best treated as a manufacturer-dependent chassis DTC. Its exact meaning can vary by manufacturer, although GM service information specifically defines it as Base Brake System Pressure Circuit/Sensor High. 4
Can a bad brake pressure sensor cause C0139?
Yes. A faulty pressure sensor can produce an incorrect high signal. However, the wiring, connector, 5-volt reference, low-reference circuit, and EBCM should also be tested.
Can wiring cause C0139?
Yes. A short to voltage, damaged wire, poor connection, corrosion, or another circuit fault can produce an abnormally high pressure-sensor signal.
Can C0139 turn on the ABS light?
Yes. C0139 is associated with the ABS/EBCM system, and warning indicators or stability-system messages may appear depending on the vehicle.
Can C0139 disable traction control?
Yes. On applicable GM systems, the EBCM can disable traction-control and vehicle-stability functions while the fault is active. 5
Does C0139 mean the ABS module is bad?
No. An EBCM or hydraulic-module fault is only one possibility. The pressure sensor circuit, reference voltage, wiring, connectors, and sensor signal should be tested before replacing the module.
Final Takeaway
C0139 indicates a high condition in the base brake system pressure circuit/sensor on applicable GM vehicles. The fault can involve the brake pressure sensor, signal wiring, connector, reference circuit, EBCM, or hydraulic brake-control assembly.
The most reliable diagnosis is to scan the ABS module, check related DTCs, monitor brake-pressure live data, inspect the wiring and connectors, verify the reference and signal circuits, and test the EBCM/BPMV only after the basic electrical checks have been completed.