Audi A6, A8, S6 & S8 Adaptive Cruise Module: Decoding Failures and Component Protection (2003-2010)

Is This Guide for Your Vehicle?

This article applies to the Adaptive Cruise Control (ACC) module, Audi part number series 4E0907468, used in the following vehicles equipped with ACC (option code 8T4):

• 2004-2008 Audi A6 (C6 platform)
• 2003-2010 Audi A8 & A8 Quattro (D3 platform)
• 2007-2008 Audi S6 (C6 platform)
• 2007-2009 Audi S8 (D3 platform)

Important: If your vehicle only has standard cruise control (without the ability to automatically adjust speed based on traffic), this guide does not apply to your car. The ACC system is a specific, optional feature.

Symptoms of a Failing ACC Module

When the ACC module fails, you will lose all adaptive cruise and forward collision warning functions. The most common symptoms include:

• "ACC and braking guard unavailable" Message: This is the most frequent error message displayed in the instrument cluster. It indicates the system has detected a fault and has shut down.
• "ACC sensor blocked" Message: While this can be caused by snow, ice, or heavy dirt on the front radar sensor, a persistent message on a clear day often points to an internal sensor or module failure.
• Red Cruise Control Light on Startup: During the instrument cluster's self-test when you turn the car on, the cruise control symbol may briefly flash red, indicating a stored fault in the system.
• System Will Not Activate: The ACC system will refuse to turn on when you press the button on the control stalk, with no response or an immediate error message.
• Diagnostic Trouble Codes (DTCs): A scan with a proper diagnostic tool like VCDS or OBDeleven may reveal specific fault codes. Common codes related to this module include:
  • C110300: Adaptive Cruise Control Sensor Misadjusted.
  • C12EBF1 / C12EB92: Laser/Radar for adaptive cruise control, malfunction.
  • 12032: Sensor for Automatic Distance Regulation; Incorrectly Positioned.

Known Issues, Recalls, and Technical Service Bulletins (TSBs)

Recalls

There are no active recalls from the NHTSA specifically for the Adaptive Cruise Control module on these vehicles. However, these models were subject to other significant recalls you should be aware of:

• Takata Airbag Recalls: A major recall campaign affected the 2005-2008 Audi A6 and S6, as well as the 2003-2010 A8 and S8, for faulty passenger airbag inflators that could rupture. Ensure this critical safety repair has been performed on any vehicle you own or are considering buying.
• Sunroof Glass Detachment: Certain 2007-2009 Audi A8 and S8 models were recalled because the sunroof glass panel could detach from its frame while driving.

Technical Service Bulletins (TSBs)

Audi has released software updates that can address certain ACC malfunctions. In some cases, a TSB addresses intermittent "unavailable" messages that can be fixed with a software flash at the dealer, rather than a full module replacement. If you are experiencing issues, it is worth checking with an Audi dealer to see if any TSBs apply to your vehicle's VIN before spending money on parts.

Buying a Used ACC Module: A Step-by-Step Guide

Buying a used OEM module can save you over a thousand dollars compared to a new one, but you must follow these steps carefully.

1. Confirm Your Car Has ACC: Check your cruise control stalk. If it has a small rocker switch on the end to adjust following distance, you have ACC. You should also see a square radar sensor in the lower front grille.
2. Match the Part Number: The primary part number is 4E0907468. The letter at the end (B, C, D, E, F, G, H) indicates revisions. While later revisions are often backward-compatible, it is safest to match your original part number exactly or consult with a parts specialist. The 'H' version is often specified for D3 A8/S8 models.
3. Inspect the Unit: When you receive the used part, carefully inspect the electrical connector pins for any signs of green or white corrosion, or bent pins. Check the casing for cracks or signs of water damage.
4. Budget for Programming: Do not forget to factor in the cost of programming at the dealership. Call your local Audi dealer beforehand and ask for the price to "remove Component Protection and calibrate a customer-supplied used ACC module." Prices can vary significantly.

Replacement Overview and Location

The replacement process involves two distinct parts: the control module and the radar sensor.

• Control Module (J428): On the Audi A8/S8 (D3), the control module itself is located inside the car, typically behind the glove box in the passenger-side footwell area. Access requires removing the glove box assembly.
• Radar Sensor: The radar sensor is located at the front of the vehicle, usually in the lower part of the grille. In some designs, the module and sensor are integrated into one unit.

While the physical swap of the module can be done by a competent DIY mechanic, the vehicle is not drivable in a fully functional state until it has been programmed and calibrated. Calibration may be required to ensure the radar is aimed correctly, a procedure that requires special alignment tools.

Cost Comparison

Frequently Asked Questions (FAQ)