A longtime customer brought in his 2006 Toyota Sienna handicap-accessible van last month. He said the passenger-side sliding door was not operating properly; it did not open most of the time.

The Sienna’s sliding doors are a complicated system that uses motors, switches and four different control modules. The body control module (BCM) has to communicate with all of the door switches, the passenger-side sliding-door module, the driver-side sliding-door module and the rear-hatch module. Before that can happen, both sliding doors have to be adapted – manually or with the factory scanner – so the system knows when they are in a fully open or fully closed position. Once adapted and the components are communicating, the doors will open with a push of a switch.

The fact that this van has been converted for the disabled means it includes a complicated ramp system overlaid into controls, modules and motors.


It is always difficult to troubleshoot a large electrical system – and when there is an aftermarket system installed, it can create unexpected obstacles. But at least we have the information and factory tools to help us.

The customer took the car to the handicap repair center first, thinking the problem may be in its system, but the repairperson said the system was working properly and the passenger-side door module needed to be replaced.

Once the van was in our shop, we started our check. The scanner didn’t reveal any diagnostic trouble codes.

We then checked the battery voltage. If the voltage drops too low, the door adaptations could be lost, so the battery was the logical place to start. During the battery test, we discovered that both battery terminals were loose, so we tightened them and performed the load test. The battery load tested at 9.9 volts at 300 amps for 15 seconds. A reading of 9.9 volts under load is good, but we still charged the battery.

We then moved on to the door adaptations, but there was no communication. While the scanner was connected, we pulled codes again and got something new: code B1216 (multiplex communication system rear door ECU communication stopped).

We followed that test plan, which led us back to the battery. We used a different battery tester to check each battery cell and found one cell was worn. After replacing it, we adapted the side doors and ran a functional test. The doors worked one time, then again stopped working.

We ran the next test plan and could see we could not communicate with the passenger-side door module. We pulled out the wiring diagram and did a pin-by-pin check of the system. We could see that the driver-side door control module needs to communicate with the passenger module for the system to perform normal operations.

We could not gain access to the passenger-side door module until the handicap ramp was removed, however. The customer had the handicap company pick up the van from our shop and remove the ramp. After gaining access to the passenger-side module, we started testing again and confirmed all the signals into the passenger-side module. That’s when we knew we had to replace the passenger-side door module.

After receiving the module two weeks later, we installed it and found that communication was limited – we could see the module but not communicate with it. We performed the adaptation and tried to open the doors. The driver-side and rear tailgate operated and were communicating with the BCM, but not the passenger side. We checked the communication buss from the BCM to the right door; the pattern looked normal.

Next, we checked the power and ground wires to the right-side door module. Although the power wires were not shorted, we thought they may not be able to carry a load. That led us to add a load (bulb) to the power and ground wires to verify if the circuit could carry a load. It was possible that we had voltage, but not enough.

During the first test, everything looked good. We then tested each command from the BCM to the door modules and found that the left-side door’s on/off switch was stuck on off. We then ohm-tested the wire from the right-side door module to the switch – it tested OK – and verified that the right-door switch worked.

Diagnosing the problem

At this point, we started to tear our hair out. We started checking all the power and grounds wires again for the capacity to carry a load. While we were testing the blue/white wire (connector P27 pin 10), we found an intermittent voltage drop. The voltage at pin 10 was 2 volts. We tested the wire harness, and the voltage fluctuated between 2 and 3 volts. We jumped power to pin 10 and the right-side door went online. The driver-side module now could see the switch from the passenger side.

We then chased the wire from pin 10 into the main body wire harness. There are two main junctions (connectors J35 and J36) – in the right-front kick panel and in the dash. We disassembled the right-side front kick panels and covers to gain access to the junctions, finding a combination of factory and aftermarket wire harnesses. After gaining access to the connectors, we traced the power supply (blue/white wire) into the main connector. Once we disconnected the connector, we found severe water damage. The majority of the 34 pins were corroded beyond repair without a replacement connector.

We cut both connectors apart and painstakingly rewired the harness, which allowed us to communicate and command the operation of the doors.

But the repair doesn’t end there: An aftermarket sensor that sees the passenger-side door motor was also defective. We sent the car back to the handicap repair facility to replace the sensor.

This car was a challenge, spending at least four weeks in the shop, and it took my entire team to solve the problem.

Matt Pataky owns Sunnyvale Foreign Car Service, 15 Pioneer Way, Mountain View. For more information, call (650) 960-6988, email sfcsmv@gmail.com or visit sunnyvaleforeigncar.com.

(0) comments

Welcome to the discussion.

Keep it Courteous. Be respectful, truthful, and use no threatening or hateful language.
Be Proactive. Use the 'Report' link on each comment to let us know of abusive posts.
Share with Us. We'd love to hear eyewitness accounts and the history behind a news event.
Read our full comments policy: losaltosonline.com/comments