Auto trans randomly shifts into low gear?

[dlrotter]

My 07 Yaris randomly shifts into low when driving on the highway. The shift indicator will show D but randomly also shows LOW at the same time... Can it be the oil? It looks good and no leaks. Someone said it could be the "Park Neutral Position Switch". Where is it? Any other ideas?

[CTScott]

I would suspect the switch, particularly if it only shows the wrong gear and doesn't suddenly start screaming at high RPM. The switch is part of the transmission.

[dlrotter]

Oh yea. It does actually shift into low gear causing engine to scream. More thoughts?

[CTScott]

Oh yea. It does actually shift into low gear causing engine to scream. More thoughts?

Yikes! The fact that you see the indication of gear change on the cluster says that it is most likely not an internal issue, but rather an external one, perhaps with the linkage to the park/neutral switch assembly (which feeds the gear selector position info to the ECM). It may be as simple as one of the bolts having come loose where the shift cable meets the selector.

47880

[dlrotter]

Thank you for the feedback and diagram! I'd does seem like it may be a sensor telling it to shift to me. Have any leads as to where to pick up the sensor if it is the prob after I check linkage? Dealer was about $580! O'Reilys a little cheaper...

[tooter]

Thank you for the feedback and diagram! I'd does seem like it may be a sensor telling it to shift to me. Have any leads as to where to pick up the sensor if it is the prob after I check linkage? Dealer was about $580! O'Reilys a little cheaper...

Just a guess... but isn't there something that senses a loss of manifold vacuum signalling a heavy engine load that downshifts the transmission? Maybe the vacuum line from the manifold to the engine load sensor is leaking. If the sensor lost its vacuum signal, it would drop the transmission into low because it would behave like the gas pedal was pushed to the floor.

(ok CT... now you can tell me how wrong I am again :laugh: )

[CTScott]

^LOL - The fact that the cluster display shows the gear changing, means that it is happening by external, rather than internal influence.

As for finding the selector switch, junkyards would be the place to look. An entire transmission can be had for $350 on eBay.

[dlrotter]

Ok I'll look at junkyards too. Tooted, I was thinking the same way at first too. But when driving more it randomly changes. I can barely be giving it gas basically just coasting at 55 mph and randomly shift to Low. (I wish the car had a tach for curiosity sake...) T hat motor can scream.

[dlrotter]

I found my problem! There was water in the connector. Looked like once water got in. There is not a was for it to drain or evaporate. Cleanned it up and so far working ok.