ACC or cruise control not activating or faulty after coding or retrofit

How to recognise the problem

Typical symptoms after a retrofit or coding change: ACC cannot be selected or switched on, the dash shows Speed Limit instead of cruise, the ACC switch reports an implausible signal, the radar reports no communication or sensor misaligned, engine or ABS log incorrect coding, or ACC works but menus, distance settings or cluster graphics are missing.

Some behaviour is normal. On an Audi A3 8V with lane assist, side assist or traffic sign recognition fitted alongside ACC, the cluster shows the generic 'Assistent' label instead of 'ACC' by design. Similarly, a car with ACC fitted has no separate non-adaptive cruise option; owners report it only appears if ACC is coded out.

• ACC unavailable or will not engage after radar retrofit
• Cruise buttons dead or EPC light after steering wheel swap
• Faults in 01, 03, 16 or 13 immediately after coding
• Errors that only appear after driving some distance
• ACC works but menu entries, distance display or curve/speed-limit functions are missing

Before changing anything

Several fixes below change long coding, adaptations, equipment codes (FEC/SWaP) or module software. Before starting, record the current train and part number of every module involved, save a full scan and back up coding and adaptations of 01, 03, 13, 16, 17, 19, A5 and 5F. Keep a stable battery supply connected throughout. Do not flash any module or write a dataset unless it matches the exact configuration of the car.

• Note the train and part number of the head unit and each assistance module
• Back up coding and adaptations of every module you will touch
• Connect a stable power supply
• A genuine, reliable diagnostic interface is recommended; clone interfaces were suspected in several failed cases

Likely causes

The notes point to a handful of recurring causes. Most cases come down to one module still being coded for the old configuration or to hardware that does not support the requested function.

• Gateway multi-function steering wheel variant still set to CCS (speed limiter) instead of ACC
• Steering wheel module or stalk not coded or not matching the ACC/limiter layout
• Fast functional settings (FFS) not run after gateway replacement, so FECs and CCS are missing
• ABS unit or wheel sensors not supporting follow-to-stop, or ABS coding not matching the radar coding
• Radar carrying the donor car's equipment code, using an unsupported coding value, or misaligned
• Wiring errors between radar and gateway or between steering wheel buttons and ECM
• Conflicting systems still coded, such as a parking system in module 13 or front assist coding
• Gateway, cluster or head unit not supporting the function or display

Step 1: Check hardware and wiring

Confirm the physical parts before chasing coding. Owners report that a Passat B8 with front assist needs no extra wiring for ACC, only the correct steering wheel buttons, while a 2016 Superb with front assist lacked the ACC stalk.

• Confirm the correct stalk or steering wheel buttons for ACC are fitted
• On a radar retrofit, check the CAN wiring; one suggestion for an A3 was radar pins 2 and 3 to gateway pins 7 and 17 (extended CAN), unconfirmed
• If the ECM reports an implausible ACC switch signal, check the button-to-ECM pin assignment for that specific engine ECU
• Check the gateway part number; one report states a virtual cockpit retrofit on an A3 8V needs a 5Q0 AM or 3Q0 gateway, otherwise ACC is lost
• Verify the radar is physically mounted at the correct angle

Step 2: Gateway, steering wheel and engine coding

This is the most frequently confirmed area. After fitting a Tiguan wheel to a Golf 7 with gateway 3Q0 907 530 H, cruise only showed Speed Limit until the gateway adaptation ENG118779 (MAS06614, multi-function steering wheel variant) was changed from CCS to ACC and the speed limiter was closed in 01. Where a gateway was replaced (5Q0907530AC with a 5Q0953507GD steering wheel), the ECM cruise fault cleared after running FFS and restoring the FECs.

If enabling the speed limiter alongside ACC fails, one confirmed (but disputed) method is to enable the limiter in the engine and then change the steering wheel module bits one at a time, saving after each, rather than setting several bits in one save; try a different order if an out-of-range error appears.

On an A3 8V DSG with EPB, invalid coding faults in 01 cleared after locking the car and leaving it 10 to 15 minutes so the CAN bus could go to sleep.

• Set the gateway multi-function steering wheel variant to match the hardware (ACC or CCS)
• Code the steering wheel module (16) for ACC, then code engine and ABS for ACC
• Run FFS after any gateway replacement and confirm FECs are restored
• Make sure stalk and coding agree; on a Q2, ACC only worked after the limiter was removed from coding to match the stalk
• Lock the car and let the bus sleep 10 to 15 minutes, then clear faults and recheck
• For a speed limiter with ACC, change steering wheel bits one at a time

Step 3: ABS and follow-to-stop

If the ABS rejects the change with Out of Range (VCDS) or Function not available (ODIS), the ABS unit does not support the requested ACC follow-to-stop setting. The confirmed approach is to adjust the ABS coding byte by byte until it is accepted, and to use a radar coding that the ABS supports.

Errors that appear only after driving, roughly 10 km in one case, were attributed to wrong ABS wheel sensors for the kit. Check whether the car has direction-sensing wheel sensors before changing ABS bytes; a wheel speed sensor error after an ABS change on a 2020 Polo was linked to this. Advice on enabling stop and go on a SEAT Leon by changing ABS bits or updating ABS software is disputed.

On manual transmission cars, ACC without follow-to-stop has a low-speed restriction and asks the driver to brake at low speed; this is expected behaviour.

• Make ABS coding match the radar coding
• Change ABS coding in small steps if the module rejects it
• Verify the correct direction-sensing wheel sensors are fitted
• Expect a minimum operating speed on manual cars without follow-to-stop

Step 4: Radar coding, equipment codes and calibration

A radar taken from another car (for example 5Q0907561N from a wrecked Golf 7) still carries its original equipment code and needs its FEC changed to suit the new car before following the coding guide for that part number.

On a 3QF907561D radar, coding was accepted without errors but pACC did not work; the suggested cause was a coding value higher than the engine ECU supports, with a lower value such as 8050 proposed instead of 8140. This is unconfirmed.

For a 'front assist/ACC unavailable' message with an intact radar, a confirmed fix was to park about 1.2 m from a wall, run the ACC calibration in module 13 basic settings, clear the fault and test drive. Where calibration was lost repeatedly with fault C110300, the radar was physically mounted at the wrong vertical angle; the angle values were zeroed in developer mode and the mounting corrected.

Other radar-side fixes reported: a fault after an ACC retrofit on a 2017 Tiguan (2Q0907572R) was addressed by changing the radar adaptation 'Reduction' from 0 to 38 (suggested). Errors after retrofit that disappeared when lane change assist was decoded were traced to the parking system (APS); disabling it in module 13 coding was confirmed. If front assist reports incorrect coding after the retrofit, check the AWV-related coding.

• Change the equipment code on donor radars
• Use a radar coding value the engine ECU supports
• Calibrate the radar with the car square to a wall
• Correct the physical mounting angle if calibration keeps being lost
• Remove conflicting systems such as APS from module 13 coding

Step 5: Menus, cluster and head unit display

If ACC works but the active info display shows the car symbol stuck behind the lead-car stripe, owners confirmed that the FPK function was set to not installed in ACC long coding (radar 5Q0907572K); coding it to installed fixed the display. The same FPK function also governs curve view on some cars, which additionally depends on cluster version.

Front assist missing from the AID menu was fixed in one confirmed case by activating menu_display_pdc in 5F. On an MST2 unit (MST2_EU_VW_P0876D) the ACC menu was restored, as a suggestion, by activating menu_display_ACC, menu_display_ACC_over_threshold_high and ACC_ACC_0x05 in the 5F car function adaptations. After any 5F change, reboot the module; otherwise it may list options that cannot be activated.

A 5F coding error during a radar retrofit was traced to a unit reflashed from Audi to VW without correct EEPROM repair. On a pre-facelift A3 8V cluster the distance setting could not be changed; a facelift cluster was the suggested fix.

• Set FPK to installed in ACC long coding for AID/cockpit distance graphics
• Activate the relevant menu_display channels in 5F adaptations
• Reboot 5F after each change
• Check cluster version if distance or curve graphics are missing

Predictive ACC (pACC) specifics

pACC needs the radar, camera, head unit and cluster to support it. Owners report that camera 3Q0980654H is older than the variants that introduced pACC and that the L variant behaves better. Older software that only uses old SWaP packages may make some radar and camera combinations impossible. In some regions pACC is not supplied, and missing country HMI data was blamed for an inconsistent pACC display on MIB2.

For pACC that does not slow for limits or curves, suggestions include confirming all SWaP entries are active, activating the speed-limit and curve assistant channels in 5F, and checking the dataset. On an MST2 unit (MST2_EU_VW_P0635D_MU0757) with a missing pACC tolerance setting, the radar software or dataset was suspected rather than the head unit firmware; check radar coding before updating the head unit. Whether a virtual cockpit is required for pACC is disputed.

• Verify camera and radar variants support pACC
• Confirm SWaP/FEC status before changing coding
• Check radar coding and dataset before touching head unit firmware

Stop and go hold time

If ACC stop and go only holds for about 3 seconds before pulling away, two confirmations report that setting pretrigger reduction to deactivated in ACC coding lengthens the ready-to-go window to roughly 8 to 10 seconds.

• Locate the pretrigger reduction setting in ACC coding
• Set it to deactivated and test

What did not help

Several approaches failed or remain unresolved and are worth avoiding or treating with caution.

• Writing a radar dataset without matching the exact configuration left lane assist and radar menus missing; restoring the original dataset was needed
• Copying a pACC-enabled dataset to a China Passat with a retrofitted MIB did not activate pACC
• A non-stock navigation unit with component protection active kept pACC inactive despite bus resets and setting changes
• An intermittent databus fault on a Polo AW after cruise retrofit was not cured by SVM, FFS or redoing final coding
• An SVM activation error FFP0705E on an A3 8V was blamed on non-SVM-compatible head unit firmware; returning the head unit to its original software and train was suggested, but this is disputed
• Mass timeouts after an ACC and camera install were not resolved by coding modules one by one; gateway support and an unreliable interface were suspected