Recently, we had a customer bring in a 2011 BMW 328i with the Supplemental Restraint System (SRS) malfunction light on. The customer stated that the SRS light came on after she and her kids entered the car. She also said the SRS light was intermittent.
Once the car was in the shop, we connected it to the Intelligent Service Technical Application (ISTA). The code that we pulled was 93AF: active head restraint resistance too high. We then performed an ohms inspection of the passenger-side head restraint circuit using the ISTA. We found the passenger-side head restraint airbag jumped between 2.9 ohms and 9.6 ohms. The specification of that circuit is 2 ohms to 5.6 ohms. We then compared the driver’s side circuit and found it at 2.8 ohms. We called the customer and got the OK for the passenger-side headrest restraint repair kit.
After installing the passenger-side headrest restraint repair kit, we cleared the codes in the SRS system. With the ISTA still connected, we performed the ohms inspection of that circuit. The passenger-side circuit was now reading 2.8 ohms. We then test-drove the car. After the third test drive, we saw that the SRS light came on again. We reconnected the ISTA and pulled codes, receiving the same code saying the active head restraint resistance was too high. We then ran the ohms inspection of the passenger-side head restraint circuit using the ISTA. The test came back at 2.8 ohms.
This is where things got interesting. Before, the car was setting a code because the passenger-side head restraint was fluctuating between 2.9 ohms and 9.6 ohms (with a specification of 2 ohms to 5.6 ohms). Now, the passenger-side head restraint was testing at 2.8 ohms. The code should not be set.
We proceeded to disassemble the passenger-side seat. We removed the head restraint covers, the seat back covers and the upper seat belt holder. With all the covers off, we disconnected the wire harness from the floor and moved it to the passenger-side head restraint repair kit. We tested the seat wire harness. At first, the harness test was fine. We then performed a wiggle test of the wire harness and found that the wire harness would test open (shorted/broken wire). After removing the wire harness insulation, we found two broken wires.
We called the customer and got the OK to replace the wire harness. After replacing the wire harness, we ran all the post-tests again. The resistance was at 2.8 ohms. We drove the car multiple times and moved the passenger-side seat multiple times. The car is a two-door.; when you tilt the passenger-side seat forward, the automatic headrest would lower. Since the customer tilted the seat forward multiple times daily to load and unload people, the automatic headrest moved up and down every time. The frequency of this movement caused the wire harness to break.
After repairing the car, I still had one question on my mind. I wanted to know the condition of the passenger-side headrest repair kit. With it off the car, it tested open (shorted). In the end, we deduced that the shorted wire harness caused damage to the components in the headrest.
Matt Pataky owns Sunnyvale Foreign Car Service, 15 Pioneer Way, Mountain View. For more information, call (650) 960- 6988, email [email protected] or visit sunnyvaleforeigncar.com.
