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Grounding Lock Input Wire Makes Control Unit HappyPosted 3/12/2001By Paul Kujawa
Vehicle: Problem: Whenever the driver attempted to lock the doors on this vehicle - whether by key, by pushing the driver or passenger door lock button down, or by using the door lock switches at the driver or passenger door - the door locks would repeatedly try to keep locking themselves (not unlock and re-lock but keep locking). If the doors were in the unlock position, they stayed unlocked. When the driver's door lock actuator was unplugged, the problem of re-locking was eliminated and the other three door locks operated normally. This power door lock system uses a power door lock control unit to apply battery voltage and ground to all the door lock actuators in parallel. The power door lock control unit gets ground-switched inputs that tell it to lock or unlock the doors. Inside the driver's door lock actuator, there is a lock and an unlock switch to tell the control unit that the actuator did indeed move to the selected “lock” or “unlock” position. When the doors are locked, whether by key, knob or switch, the control unit sees the switch input go to ground, telling the control unit to lock all the doors. When the driver's door lock actuator moves to the “lock” position, the lock input switch inside the actuator should switch to ground and tell the control unit that the actuator went to the “lock” position. When I asked the technician to back probe and check the voltage on the blue/white wire for the lock switch inside the driver's door lock actuator, he found that the voltage was jumping all over the place when the locks were trying to keep locking themselves. I asked him to ground that blue/white wire. The locks stayed in the lock position and stopped trying to re-lock themselves. The control unit needed to see that lock switch input wire from the driver's door lock actuator go to ground and when it didn't see it, the control unit kept trying to lock the doors. When the lock input wire was grounded, the control unit was “happy” and the locks stayed locked. The technician solved the problem by replacing the door lock actuator.
Fixing Solder Joint Solves ProblemPosted 3/12/2001By Guy Dibble
The problem was an intermittent high CO reading at idle on a 1987 Mazda RX-7. While the technician was trying to diagnose the problem, he stumbled onto the fact that the car ran clean at idle until he opened the driver's door. If he shut the door, it was fine. When he opened the driver's door, he could hear the engine run differently ... and then up went the CO readings. It turned out that the “door ajar” light circuit wasn't working, and that when the door was open, there was 5v on the ground. Further investigation revealed a cracked solder joint on the printed circuit for the warning light panel. Once the solder joint was fixed, the problem went away. Here's what was most likely happening: The exhaust overheat sensor circuit was getting voltage backfeed, causing the ECM to think the exhaust was overheating - so it took away the port air injection and enriched fuel mixture at idle, to try to cool down the catalytic converter. RX-7s ... enjoy the challenge!
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