Issues with brake light switch (12 Viewers)

[arod85]

Hello everyone, I have a 91 fj80 3FE motor with 180k on the clock. I’ve been having the stuck in park issue and after doing some ih8mud digging and trouble shooting. I’ve narrowed it down to the brake light switch. Unfortunately the OEM part is no longer available, I bought one from my local parts store and it didn’t solve the main shift out of park issue, but it did improve how my transmission shift from park to drive or drive to park. I no longer have that hard clunk. It also improved my braking, before the truck would stop and go almost as if I was rapidly pressing and releasing the brake peddle. Didn’t know all these symptoms could be related, Unfortunately after replacing the switch now the rpm drop down to around 700 or below and has a rough idle when in drive and the peddle is pressed, for instance at a red light or stop sign. This was never the case prior to replacing the switch. I have the feeling due to it not being an OEM part the switch is not communicating correctly with ECM causing the rough idle. Any body have any idea where I can possibly find an OEM switch or a switch from other models that might be interchangeable? Thanks again for the support!

 

[NeverFinis]

Time to get the EWD for your model.

The brake switches I am aware of are fairly simple. They either are a simple switch to ground, or a switch to power. I have no idea what a 91 fj80 uses.

The brake switch is used for many things like the Park/Neutral Safety switch and to unlock the Torque convertor in an automatic.

 

[CJF]

Unfortunately after replacing the switch now the rpm drop down to around 700 or below and has a rough idle when in drive and the peddle is pressed, for instance at a red light or stop sign. This was never the case prior to replacing the switch. I have the feeling due to it not being an OEM part the switch is not communicating correctly with ECM causing the rough idle.

Lol.

No way does the brake switch communicate with the ECM on a 91.

 

[arod85]

Lol.

No way does the brake switch communicate with the ECM on a 91.

Lmao no clue… just going based of information online after a generic search of “does brake light switch affect idle” here is what it said

Yes, a bad or misadjusted brake light switch can affect the idle of a Toyota with a 3FE engine, like those found in the Land Cruiser FJ80
. This is primarily due to the switch's electrical connections to the engine's computer (ECU) and other sensors.

 

[NeverFinis]

I mean, does your brake lights go on/off appropriately? If they do, your switch is working. Sometimes there is a secondary circuit on a brake switch. Does yours have one or two?

I mentioned torque converter because activating the brakes will cause the torque converter to unlock, if it is a locking type. Otherwise, idle could stumble coming to a stop.

 

[arod85]

I mean, does your brake lights go on/off appropriately? If they do, your switch is working. Sometimes there is a secondary circuit on a brake switch. Does yours have one or two?

I mentioned torque converter because activating the brakes will cause the torque converter to unlock, if it is a locking type. Otherwise, idle could stumble coming to a stop.

Lights work fine. But I still have the not shifting out of park issue. The brake fuse are fine, brake lights work that’s why I’m leaning toward the brake light switch. My cruise control also isn’t working and from the research I’ve done is also a key indicator of bad brake light switch.

 

[NeverFinis]

From looking at a 91 EWD, your stop light switch is very simple, like most. If you see your brake lights coming on just as you are hitting the brakes, then it is working. I would inspect the wiring in case something is damaged, or disconnected.

Your shift lock ECU controls shifting out of park.

It has 3 inputs:

1) 12V from the stop light switch
2) 15A ECU-G fuse
3) 15A CIG fuse.

Check those fuses. This is just from a 91 EWD, which might not match yours.

 

[arod85]

From looking at a 91 EWD, your stop light switch is very simple, like most. If you see your brake lights coming on just as you are hitting the brakes, then it is working. I would inspect the wiring in case something is damaged, or disconnected.

Your shift lock ECU controls shifting out of park.

It has 3 inputs:

1) 12V from the stop light switch
2) 15A ECU-G fuse
3) 15A CIG fuse.

Check those fuses. This is just from a 91 EWD, which might not match yours.

View attachment 4006278

Thanks for the info. Took a look at the fuses this morning all of them seem okay non are blown. This would indicate the wiring is good right? If there were to be a short somewhere then it would blow the fuse correct? Apologies for the dumb question I have little knowledge on electrical.

 

[NeverFinis]

No, wiring isn't necessarily good if fuses are still good. I would ohm out the wiring to check. A short to ground would blow a fuse, but a break in the wiring would not.

I would inspect and test all the wiring between the brake switch and the shift lock control and the ECM.

There is a noise filter as well, shown in the circuit to the ECM.