A/T OIL TEMP light won't go off (1 Viewer)

[richmondbob]

On today's episode of Fok Me ... AT oil was down a bit couple weeks ago tripping the warning light on my '97 NA spec gasser 80. All good after pulling over to top off the oil but warning light's still on. Checked levels again and still good. Disconnected battery and warning lights still on after reconnecting. So, anyone know where and how hard it is to replace the sensor?

(pic for you don't want to see this on your dash)

 

[KC masterpiece]

Sensor is on the passenger side of the trans if recall correctly. Very easy to replace. 5 min job. I had mine do the same thing a few months ago and I knew my temps were fine. Ended up being a bad sensor and I just swapped mine out instead of troubleshooting since I had a spare trans in the garage.

 

[bhsdriller]

pull the bulb

 

[Kernal]

Toyota recommends with any electrical system/glitch to first disconnect the harness from the sensor and reconnect to see if that fixes the issue (if it was due to micro-oxidation or corrosion betwen the contacts). I generally spray both sides with electronics/contact cleaner while it's apart then snap the harness back to the sensor. Worth a try maybe.

FWIW

 

[bicycleagent003]

Anyone know at what temp F the light comes on? I'd love to have a real time number on that, though not quite enough to install a sensor.

 

[spikederailed]

Anyone know at what temp F the light comes on? I'd love to have a real time number on that, though not quite enough to install a sensor.

Way too damn hot. From the A442F transmission service manual.

 

[gummycarbs]

@richmondbob obvious question: are any other lights on? The A/T Temp light comes on as part of the "Christmas tree" to warn of low voltage. In that case, the red square by the voltmeter will be on, too.

 

[Dusten]

Way too damn hot. From the A442F transmission service manual. View attachment 2959129

Holy Christ. By 302* that things cooked.

 

[Dusten]

Those sensors generally close at a set temp and short to ground, triggering the light.

Pull the sensor and use a multimeter to ohm it. It should read open, or very high resistance at room temp. If it's closed or shorted, it's bad. If the sensor tests good, there's a short elsewhere.

 

[SmokingRocks]

worthless light IMO, just like the factory coolant gauge.

No idea why Toyota made the temp setting this high. Perhaps it's because it's measuring from the outflow to the cooler, and the oil in the pan should be a bit lower than that temp.

 

[bicycleagent003]

Yeah, agreed, 302* is pretty darn hot. I think mine came on once, I can't quite recall. But I'd freak out if that thing was coming on routinely.

 

[richmondbob]

Sensor is on the passenger side of the trans if recall correctly. Very easy to replace. 5 min job. I had mine do the same thing a few months ago and I knew my temps were fine. Ended up being a bad sensor and I just swapped mine out instead of troubleshooting since I had a spare trans in the garage.

Cheers. I'm having one ordered. Parts take a bit in Canada.

Toyota recommends with any electrical system/glitch to first disconnect the harness from the sensor and reconnect to see if that fixes the issue (if it was due to micro-oxidation or corrosion betwen the contacts). I generally spray both sides with electronics/contact cleaner while it's apart then snap the harness back to the sensor. Worth a try maybe.

FWIW

Good call. I'll be spraying both ends when I install the new sensor.

@richmondbob obvious question: are any other lights on? The A/T Temp light comes on as part of the "Christmas tree" to warn of low voltage. In that case, the red square by the voltmeter will be on, too.

Nope, no other lights.

pull the bulb

Take less time to fix it properly than take the dash apart without breaking anything

 

[Kernal]

If the ATF did reach that temp you'd of course want to do a complete fluid exchange/flush ASAP. Rodney from Wholesale Automatics in Australia (where they see a lot of Land Cruisers exposed to high temps) recommends synthetic ATF and a good cooler. FWIW

 

[Dusten]

Yeah, agreed, 302* is pretty darn hot. I think mine came on once, I can't quite recall. But I'd freak out if that thing was coming on routinely.

I'd freak if it ever came on. Anything above 250 and the fluid is garbage

 

[spikederailed]

I'd freak if it ever came on. Anything above 250 and the fluid is garbage

Yep, the ATF is well past varnished at that temperature.

 

[jonheld]

Those sensors generally close at a set temp and short to ground, triggering the light.

Pull the sensor and use a multimeter to ohm it. It should read open, or very high resistance at room temp. If it's closed or shorted, it's bad. If the sensor tests good, there's a short elsewhere.

On the A343F, the temp sensor is a thermistor that feeds the ECU which triggers the light. The FSM does not specify a temperature for the light, but does specify resistance vs temp in order to test the sensor.
Resistance :
20°C (68°F): Approx. 12.2 kΩ
110°C (230°F): Approx. 770 Ω

 

[Dusten]

On the A343F, the temp sensor is a thermistor that feeds the ECU which triggers the light. The FSM does not specify a temperature for the light, but does specify resistance vs temp in order to test the sensor.
Resistance :
20°C (68°F): Approx. 12.2 kΩ
110°C (230°F): Approx. 770 Ω

That's also a completely different temp range than listed for the a442f which is what I was referencing.

 

[Dusten]

On the A343F, the temp sensor is a thermistor that feeds the ECU which triggers the light. The FSM does not specify a temperature for the light, but does specify resistance vs temp in order to test the sensor.
Resistance :
20°C (68°F): Approx. 12.2 kΩ
110°C (230°F): Approx. 770 Ω

However my comment still holds water.

Resistance is very high at room temp.
It's very low(although not quite open) at 230.

If that sensor is on a table and reads very low resistance, it's failed.

 

[South Texas 97]

I just installed a A/T Temp gauge, just before the A/T oil cooler in the bottom of the radiator (the hose on the pax side is from the A/T) . Took it for a drive in 95F weather on the freeway at 65mph, the gauge showed between 130-145F while driving. When I pulled off the freeway and stopped at a stop sign, it peaked at 165F (heatsoak I guess) and then back down to 145-150F as I drove back along the freeway at 65.
I realize the sensor is not right at the A/T itself, but I figure the numbers will be relative to some base line, which should be enough to tell me if the A/T is getting overly excited.
In other threads, someone suggested using a laser Thermometer on the pan when you pull over to check the temperature. Will check and compare next time I am out and about.

 

[Malleus]

@richmondbob
I realize I'm late to the party, but...
from the A343F manual: