Transmission Selector Switch Symptoms and  Repair (P38)


Selector SwitchSymptoms and Diagnosis
Switch Description, Sources and Possible Repair/Rebuild Method
Procedure for Replacing the Switch



Photo at right: Broken selector switch after removal and disassembly into its two halves.

Description and photos on this page courtesy of Dennis Altman




Symptoms and Diagnosis
Dennis Altman reports that he started having problems with his transmission reading R when in D every now and then. Over a period of months this progressively got worse until it would read P-D-R-#-R-D-2-…rapidly for about 10 seconds, then calm down. Dennis reports: "It took longer and longer to calm down before I finally got an ETM and diagnosed it as the “XYZ” switch on the left side of the trans, on the input shaft from the shift cable to the trans. As you select gears on the shifter, the cable rotates the shaft that goes through the switch into the trans. The switch has 5 micro switches, but only 3 are used. The 3 switches send a binary signal to the trans computer to tell it which gear you’ve selected. There is a breather tube on the top of the switch, routed to the engine bay, mine wasn’t connected and the switch injested water/gunk and the switches started sticking, sending false signals to the computer. The switch finally gave up the ghost, and the car was dead, the computer thought it was in R, so no start, and it wouldn’t let the key out of the ignition."

Switch Description, Sources and Possible Repair/Rebuild Method
Dennis reports "I ordered a new switch from Atlantic British, they knew exactly what I meant, (dealer took 15 min of explaining to figure it out) and got it to me in 3 days (thanks guys).

After he had finished replacing it (see procedure below), out of curiosity Dennis drilled out the aluminum rivets holding the old switch together, and about ½ pint of water dribbled out of the little thing along with a bunch of black mung and gunk. "It might have been cleanable, but there are 2 little pins on the shaft collar that rotate the switch plate that broke off on mine, so it’s dead (might try to fix for a spare). The switch is sealed with a rubber gasket and comes apart cleanly, so if yours is just acting up, you might be able to save it by cleaning, and bolt it back together." (See photos above and below of the dismantled switch assembly).

Close-up of dismantled switch
Close-up photo of dismantled switch. Breather tube connection is at lower right of photo where wires come out.

Procedure for Replacing the Switch

Dennis reports "The swap out was simple. Remove the cotter-pin from the shift cable adaptor, -DON”T MESS WITH THE SETTING –the 10mm jamb nut and the barrel nut/pivot!!!-----(ask me how I know this..)  the nut from the shaft lever-14mm I think, and one nut/one bolt, again 12mm, that hold the switch to the side of the trans. All will be clear and simple when you crawl under and have a look (see photo below). I left the breather tube in place, to re-attach, but the new one came with a new tube, already attached-must be a common problem. My trans showed other signs of a prior removal/install (other wire connectors not mounted on their brackets, zip-ties…) so the lazyness of some anonymous mechanic cost me $350-check yours if your switch is acting up, or even if it’s not it’s a cheap save!

View of selector switch from under the vehicle
View of selector switch and cable attachment from under the vehicle.

"The new switch went on exact reverse of the old one. I taped my new breather tube to the bottom of the old one, and used the old one to pull the new one up into position. Bolt the switch into place before you reconnect the cable. To re-adjust the cable length, I put the shifter in P, rotated the input lever to P and adjusted till the holes lined up, there is play in the shifter to make sure you can get positively into gear. Move to first gear re-check fit, then re-install the cotterpin. The switch rotates on its mounts about 10 degrees, the shop manual specifies a tool/jig that bolts on, fit a pin in a slot and rotate, dangle chicken bones and chant…..I put it in reverse (it read park) and turned the switch until I heard the mirrors auto-dip. Tightened it down, crawled inside and shifted through the gears a few times to check all is well-the gearbox fault self cleared so no expensive trip to the dealer this time. No problems for over a month."

 


 

 

 

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Page revised February 2, 2012