C0002 – TCS Control Channel “A” Valve 2 (Subfault)

By Reinier (Contact Me)
Last Updated 2021-12-09
Automobile Repair Shop Owner

Table of Contents

1. What Does Code C0002 Mean?
2. Where is the C0002 sensor located?
3. What are the common causes of code C0002?
4. What are the symptoms of code C0002?
5. Get Help with C0002

What Does Code C0002 Mean?

SPECIAL NOTES: The topic of how ABS systems and related systems like Traction Control, Stability Control, Hill Start Assist, Adaptive Cruise Control, Autonomous  Emergency Braking, and others are controlled and managed by the ABS and other control units is a hugely technical one, and the details of these control systems fall outside the scope of this article. Thus, we need not delve into the complexities of these systems here, beyond saying that the electronic failure indicated by trouble code C0002 – “TCS Control Channel “A” Valve 2 (Subfault)” cannot be repaired reliably. The only reliable remedy for this code is the replacement of the ABS control unit, which requires that the replacement ABS control unit be programmed and integrated into the vehicle’s electronic systems. Therefore, we do not recommend that this procedure be attempted by non-professional mechanics. END OF SPECIAL NOTES.

OBD II fault code C0002 is a generic trouble code that is defined as, “TCS Control Channel “A” Valve 2 (Subfault)”, and is set when the PCM (Powertrain Control Module) detects an internal electronic failure in the ABS control unit, but more specifically, in the portion of the ABS control unit that controls the Traction Control System. In the case of trouble code C0002, the “Subfault” in the definition refers to said internal electronic failure.

Although traction control systems have many different names, all traction control systems do the same thing, which is to prevent wheel spin by applying modulated and selective braking forces to spinning wheels to transfer power to the non-spinning wheel(s) through the differential(s). Moreover, all modern traction control systems use the same components to prevent wheel spin that the ABS system uses to prevent one or more wheels from locking up under severe braking.

In practice, traction control can be thought of as ABS working in reverse. For instance, when one or more wheels start to spin on a slippery surface, the wheel speed sensors relay this information to the ABs control unit, which then applies a modulated braking force to the spinning wheel until its rotational speed matches that of all the other wheels. In addition, the traction control system can switch modulated braking forces between different spinning wheels at the rate of at least 20 times per second, meaning that wheel spin can be eliminated on even the most slippery surfaces, which include ice, snow, mud, and loose sand or dirt.

However, for traction control systems to work, the ABS control unit relies on accurate input data from both the engine and transmission control modules, as well as from sensors that include the steering angle sensor, yaw rate sensors, lateral accelerometers, and even pitch sensors to calculate appropriate braking strategies under all conditions. For instance, the ABS/Traction Control system might prevent gearshifts to reduce the chances of making wheel spinning worse, or the ABS/Traction Control system might prevent or limit throttle inputs, also to prevent making wheel spin worse.

Therefore, and to prevent disabling functions like gear shifting and throttle inputs unnecessarily when certain kinds of failures occur in the combined ABS/Traction control system, the ABS control unit and other implicated control modules will typically disable the ABS braking function along with other systems that depend on the ABS system to work. So, while disabling some systems and functions might make it more difficult for a driver to control the vehicle under difficult driving conditions, the driver will have full control over the vehicle, provided the failure did not initiate a fail-safe or limp mode as a safety precaution.

If the failure or malfunction in the ABS/Traction Control system did initiate a limp-mode, the normal braking system will still be available, but the transmission may be locked into one gear, while throttle responses will be severely limited. Depending on both the nature of the failure and the vehicle, one or more warning lights might also be illuminated, with the ABS, Traction Control, Adaptive Cruise Control, and Stability Control lights being the most likely to be illuminated.

Where is the C0002 sensor located?

This image shows the ABS control unit on a VW application, with the connector linking the hydraulic unit to the electronic control module on the left.

In case, as in almost all others, all of the hydraulic, mechanical, and electronic components that monitor, control, and manage the ABS and other systems that depend on the ABS system to work are contained in this unit. Note though that while many service providers claim to be able to repair these units to OEM standards, the fact is that the success rates of even the most successful repairers are extremely low- even over the short term.

Put differently, this means that ABS control units are not repairable, meaning that the only reliable repair is the replacement of the ABS control unit by suitably qualified and experienced technicians.

What are the common causes of code C0002?

Since the types of failures that cause code C0002 to be set cannot be repaired, there is not much technical information available on the possible causes of this code. Nonetheless, anecdotal evidence suggests that one or more of the following causes might cause this code, or contribute to this code setting-

• Damaged, burnt, shorted, corroded, or disconnected wiring and/or connectors in the ABS or related systems
• Corrupted software in the ABS and/or related systems, but particularly in the Traction Control system
• Abnormally high or low system voltages, such as might be caused by defects in the charging system or improper jump starting procedures
• Failing to follow the vehicle manufacture’s recommended procedures to purge air from the brake system
• Disconnecting the battery without installing a memory saving device

What are the symptoms of code C0002?

The common symptoms of code C0002 are largely similar across all applications, and could include one or more of the following-

• Stored trouble code and possibly several illuminated warning lights
• Multiple additional UXXXX (Communication) trouble codes may be present along with C0002
• ABS braking may not be available
• Several driver assists systems, such as Traction Control, Stability Control, Hill Start Assist, and Adaptive Cruise Control may be deactivated
• The vehicle may be locked into a fail-safe or limp mode that will typically persist until the fault is corrected

NOTE: For reference, note that any one or more of the trouble codes listed below may also be present when code C0002 is present on most vehicles-

• P0856 – Traction Control Input Signal
• P0857 – Traction Control Input Signal Range/Performance
• P0858 – Traction Control Input Signal Low
• P0859 – Traction Control Input Signal High
• P0880 – TCM Power Input Signal
• P0881 – TCM Power Input Signal Range/Performance
• P0882 – TCM Power Input Signal Low
• P0883 – TCM Power Input Signal High]
• P0884 – TCM Power Input Signal Intermittent
• P0885 – TCM Power Relay Control Circuit/Open
• P0886 – TCM Power Relay Control Circuit Low
• P0887 – TCM Power Relay Control Circuit High
• P0888 – TCM Power Relay Sense Circuit
• P0889 – TCM Power Relay Sense Circuit Range/Performance
• P0890 – TCM Power Relay Sense Circuit Low
• P0891 – TCM Power Relay Sense Circuit High
• P0892 – TCM Power Relay Sense Circuit Intermittent

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