Car talk Driving Electric

Mending the ID.4

What happens when a BEV is involved in a mishap? The vehicle isolates the HV power. What does it take to get it back on? That depends …

On April 7, Millennium Falcon, my VW ID.4 AWD Pro-S vehicle was involved in an apparently minor mishap with a Virginia Beach EMS vehicle exiting Independence BLVD to merge onto Northampton Blvd to respond to a call. Two vehicles in front of us in the travel lane slow and stopped blocking both travel lane and exit lane. I slowed to avoid them placing the ID.4 in the path of the EMS vehicle. Both vehicles suffered collision damage but nobody was injured. Just the two vehicles. Millennium Falcon is still being repaired!


  1. 2023-05-25 Original


  1. VW ID.4 High Voltage System Technician Self-study

Why So Long

First, insurance red tape. My insurer completely reworked the client-facing claims procedure to make it mobile friendly and to remove field people and reduce office claims team staff.

It took a week to figure out how to get an adjuster to look at the vehicle. You didn’t. There was an app for than. Then another week to get an estimate.

And another week to realize I had to walk the paper estimate to my repair shop as they were slammed and losing things coming in by E-mail. All those wickets negotiated, the earliest shop opening was May 8.

Then the shop found concealed damage, filed a supplemental estimate, and another week wait for my insurer to turn that around. So finally, Say around May 21, the vehicle goes to the VW shop for power train repair. VW issued another proposed work order that my insurer is reviewing. I’ve not seen this proposed work breakdown. What follows is speculation.

Image courtesy of VW from Reference 1
ID.4 Power Train arrangement and connections

Likely Electrical Work Needed

Reference [1] is an excellent introduction to the ID.4 HV electrical system. It shows where everything is in the vehicle and explains the HV protection features of the vehicle including the HV isolation pyrotechnics that are part of the HV contactor assembly in the battery pack. It also shows the location of the control electronics and car area networks involved in the operation of the vehicle. The language is clear and simple as it is designed for trades self-study. From this study guide, it is possible to identify the more obvious tasks the VW shop must perform to restore the vehicle power train.

Post-Mishap HV Isolation

The HV contactor assembly includes a pyrotechnic fuse that de-energizes the HVDC during an accident. This fuse is part of the HV Battery module. Shock sensors trigger this pyrotechnic fuse interrupting the HV negative rail. Reference [1] around page 35 shows the contactor and control electronics. There are two versions, one for each of the 2 battery sizes.

According to Reference [1] VW has chosen to initiate HV insolation even in minor mishaps as it is difficult to determine if a shock resulted in HV wiring damage.

Replacement of the HV isolation device is a prerequisite to further repair of the HV power system.

Battery Charger in Harm’s Way?

The battery charger is mounted on the aft end of the rear motor cradle. It is possible the mishap damaged this assembly as other components, notably the hitch, were involved. It is likely that the battery charger assembly requires replacement. This was not mentioned in the supplemental estimate that repaired the hitch and other structures between the bumper and the rear motor cradle.

Restoring High Voltage

Restoring high voltage requires replacing the pyrotechnic fuse which is not field serviceable. The SX8 module containing the fuse must be replaced as a field replaceable assembly.

Image courtesy of VW
ID.4 Battery Pack with top cover removed

A figure on Reference [1] page 32 shows the battery assembly with the top cover removed. The SX7 and SX8 modules are located in the aft compartment of the battery assembly and appear to have only top access. It appears that their replacement requires lowering and opening the battery assembly, replacing the parts, closing it, and reinstalling it in the vehicle.

This is a big task as the battery pack weighs 1100 pounds and there are many fasteners to be removed and reinstalled. Once the battery pack is out, it is hot work to replace the contactor assembly as bus bars connect it to the battery pack terminals. This is touchy work that must be performed by a hot work skilled technician.

Replacement of the contactor and reinstallation of the battery are prerequisites to further repair of the HV drive system.

Replacing the Battery Charger

The AC battery charger is located at the aft end of the rear motor cradle. this position should permit easy replacement of the battery charger if damaged. The J-1772 charging connector cable and the and DC HV charge cable connect by connectors. Assuming cable connectors are undamaged, this module is easily swapped for one that is not bent.

If the connectors are damaged, new cables must be run. Interference removal may be needed for this task.

Reference 1 shows a good arrangement diagram of the rear drive and battery charger on page 13.

Codes, codes, codes

The HV system supplemental estimate is based on the codes logged. When the vehicle was smacked, the shock sensor fired the pyrotechnic fuse to isolate the HV but this may not be a clean power cut. Additional safety devices discharge the capacitors in the front and rear motor inverter assemblies. It is likely that all of these devices logged fault codes as a result of power chatter and the power cut. These codes have to be investigated and resolved. It all has to be sorted for the vehicle to be considered safe to drive as the J632 engine control module is part of the system performing all drive control and ADAS functions.

Fuse Replacement without Dropping the Pack?

The HV safety fuse is part of the SX8 module internal to the battery pack. Bus bars connect the SX7, SX8, and the battery. The entire SX8 assembly must be replaced. Removal and installation of these bus bars is hot work.

It would be nice if the two battery control modules could be replaced without dropping the pack. It would save a big chunk of labor to pull all the fasteners, lower the pack, move it to a work table, and reinstall it. And it would eliminate hot work in the field.

Redesign of these parts to attach by connectors like those connecting the battery to the inverter assembly and provision of an under pack access plate would be required. There may be safety reasons for not taking this approach.

Image courtesy of VW from Reference 1
SX7 and SX8 modules and connection

By davehamby

A modern Merlin, hell bent for glory, he shot the works and nothing worked.