Faulty brake pressure sensor or brake pedal position sensor sending incorrect signals; Worn or contaminated wheel speed sensors causing inaccurate deceleration readings; Software glitch or outdated calibration in the adaptive cruise control module; Damaged wiring or corroded connectors between the ACC module and brake system components; A failing ABS pump or hydraulic modulator that cannot build pressure on command; Low brake fluid level or air in the brake system affecting pressure response; A malfunctioning ACC module itself, though this is less common than sensor or wiring issues

DTC codes / C08xx · Brakes, steering and suspension / C0870

C0870Adaptive Cruise Control Brake Request Performance

Q: What does code C0870 mean?

Adaptive Cruise Control Brake Request Performance. C0870 indicates that the adaptive cruise control (ACC) system's brake request signal has failed a performance check, meaning the ACC module commanded braking but the vehicle did not decelerate as expected or the brake system did not acknowledge the request. The computer typically detects a mismatch between the requested brake pressure or deceleration and what the wheel speed sensors and brake pressure sensor actually report.

C0870 indicates that the adaptive cruise control (ACC) system's brake request signal has failed a performance check, meaning the ACC module commanded braking but the vehicle did not decelerate as expected or the brake system did not acknowledge the request. The computer typically detects a mismatch between the requested brake pressure or deceleration and what the wheel speed sensors and brake pressure sensor actually report.

SystemChassis

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyProfessional

AreaBrakes, steering and suspension

Symptoms you may notice

Adaptive cruise control disengages or refuses to activate, often with a 'cruise not available' message
A warning light or message on the dashboard indicating a cruise control or brake system fault
The vehicle may brake abruptly or not at all when ACC is active, though this is less common
Often no symptoms besides the warning light, with normal driving unaffected
The conventional cruise control may still work, but adaptive features are disabled
In some cases, the brake pedal may feel different or the ABS light may illuminate if the fault affects shared components

Common causes, most likely first

Faulty brake pressure sensor or brake pedal position sensor sending incorrect signals
Worn or contaminated wheel speed sensors causing inaccurate deceleration readings
Software glitch or outdated calibration in the adaptive cruise control module
Damaged wiring or corroded connectors between the ACC module and brake system components
A failing ABS pump or hydraulic modulator that cannot build pressure on command
Low brake fluid level or air in the brake system affecting pressure response
A malfunctioning ACC module itself, though this is less common than sensor or wiring issues

How to diagnose and fix it

Scan all modules for stored codes and freeze-frame data to confirm C0870 and identify related faults
Inspect brake fluid level and condition, and check for leaks in the hydraulic system
Test the brake pressure sensor and brake pedal position sensor with a scan tool to verify live readings
Check wheel speed sensors for debris, damage, or erratic signals using a graphing scan tool
Inspect wiring and connectors between the ACC module, ABS module, and brake sensors for corrosion or damage
Perform a calibration or software update on the ACC module if applicable, following manufacturer procedures
If all else fails, diagnose the ACC module and ABS pump with advanced testing, and replace only after confirming faulty operation

Before you replace the ACC module

A weak or failing battery can cause voltage drops that trigger C0870 because the ACC module and brake sensors are sensitive to low voltage during cranking or high electrical load.
After any brake system repair or fluid service, the ACC system may need a recalibration or a relearn procedure, and skipping this step can set C0870 even though the hardware is fine.
Debris or rust on the tone ring of a wheel speed sensor can cause intermittent signal loss that only shows up during ACC braking, not during normal driving.
A misadjusted brake pedal position sensor, often after pedal work or a floor mat replacement, can make the ACC module think the driver is braking when they are not, setting this code.
Some vehicles set C0870 when the adaptive cruise control radar is misaligned or blocked, because the module cannot verify brake request performance without a clear forward view.

Can I keep driving with C0870?

You can generally drive the vehicle normally because the conventional braking system remains fully functional, but adaptive cruise control will be unavailable and should not be used. Avoid relying on cruise control until the fault is repaired, and have the system diagnosed promptly to prevent any unexpected braking behavior.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

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