BACKYARD MECHANIC: Unhappy owner feels like throttling sensor

Hey there, time traveller!
This article was published 10/12/2010 (5409 days ago), so information in it may no longer be current.

QUESTION: I have a 2000 Subaru Legacy Wagon, Brighton edition. It just turned 100,000 km but for the past year or so it has been intermittently throwing a CEL code P0122, Throttle Position Sensor low voltage almost once every two weeks. It is erratic in that the CEL will clear itself after one or two restarts. We have replaced the TPS sensor and carefully adjusted it within spec and it still has been acting erratically.

We recently replaced the grounds at the battery and the engine block to firewall without success. It works great for four or five days and then again starts bucking and hesitating and throws a P0122 code. Shut it off let it cool and restart, the CEL clears and you are good for a few more days. Do you think it could still be a ground issue or would you suggest replacing the TPS again?

ANSWER: The throttle position sensor shares a ground connection with the manifold absolute pressure (MAP) sensor and pass through connector B21 and B83 before going to the engine computer. Connector B21 is in the engine compartment and is a Grey 20-way connector. Connector B83 is under the passenger side of the dash and is a Blue 12-way connector. This connector is a common ground and shield wire junction point for many of the sensors. A poor connection at either of these connectors could set the intermittent code you are getting. The throttle position sensor will set a code much faster than other sensors, as the computer runs tests on it continuously when the key is on.

The problem could also be with the ground connection for these sensors back at the engine computer connection or a poor connection on the sensor signal wire to the engine computer. This may be a difficult problem to spot. Sometimes all it takes is to disconnect and reconnect the connectors and the terminal movement scrapes through any corrosion to create a good connection. When you have the connectors apart, look carefully for any white deposits on terminals. This is corrosion and it can be cleaned with a rubber eraser if you can get at the terminal. There are electrical terminal cleaning sprays that will also work. I usually find these sold through electronics parts suppliers although some automotive supply shops carry it.

Also look for any terminals that may be pushed back out of the connectors. The plastic connector may be pushed together tight but the metal terminals inside are not connecting. I don’t think this problem is with the Throttle position sensor itself. It sounds like you are on the correct track with ground connections.

QUESTION: The right rear door won’t unlock on my 1997 Civic EX, either from the master switch (on driver’s door) or even trying to pull up on the button (on right rear door) itself inside the car. As a result, I can’t even remove the door panel to change the actuator. The other three power door locks work. Does this sound like a broken actuator? How would I go about opening the door?

ANSWER: It sounds like something has broken in the latch mechanism inside the door. Even if the electric lock wasn’t working, you should still be able to unlock the door with the mechanical lock button. To access the door latch mechanism, you have to remove the door panel. This will be difficult to do without damaging the door panel. Start by removing the back seat cushion so you have better access. Then you will need to remove any screws and handles. Finally, you need to pry the door panel loose from the plastic push clips. I have made some custom bent tools out of old screwdrivers to attempt this.

With the door panel off, try forcing the linkage on the latch with a pry bar. Removing the window glass can provide additional working room. If the latch won’t release, you have to drill out the mounting screws from inside the door. This is tricky. With the latch loose, you can usually get it to unlatch and open the door. Before trying any of this, try pushing hard on the door in the latch area while someone else works the mechanism. Be careful to push in a braced area so you don’t bent the door. Sometimes that will open a stuck latch.

 

Jim Kerr is an experienced mechanic, instructor and member of the Automobile Journalists’ Association of Canada.

kerr.jim@sasktel.net