CCDave

I used the FSM to test ECT ECU on my 87 4Runner 22RE-T with A340H transmission and I found a -7v difference between the FSM and actual volts for TH+ and TH- (the AT Fluid Temp Sensor wiring). My reading is 4.94v (both at both the ECT ECU and at the temp sensor connector), instead of the 12v stated in the FSM. I swapped in a spare ECT ECU and spare Fluid Temp Sensor and the reading was still 4.94v. The other ECT ECU voltage test readings (throttle valve, brake pedal depressed, shifting positions, etc.) all match the FSM. I'm stumped. Any ideas on what might cause the 7v loss?

RASALIBRE

scope103

Why don't you post a shot of the FSM, where it describes the test. It seems unlikely to me that the ECT Computer would put 12v BETWEEN TH+ and TH-. Were you, instead, measuring TH+ to ground, and TH- to ground? (That would be two measurements.)

CCDave

I checked and these's no voltage drop in the wiring from the ECT to the Temp Sensor.

CCDave

Here's the test table in the FSM. I ran the test with both a Denso type and an Aisin type. Possible misprint?

wyoming9

iTrader: (1)

Just what problem are you trouble shooting ??

At What temperature does the FSM state you should get 12 Volts ??

Are you sure you need to measure voltage ??

Most thermisters change resistance as the temperature changes

Just how are you trying to measure this ??

Engine running ?? Shutoff ??

CCDave

Temp is not relevant in this test per FSM (the volt test table 2 posts up show that there is no measuring condition for the volt test).

Yep. Per FSM (see volt test table in above post). There is a separate resistance check, and the sensor checks good.

Mmultimeter set to measure volts, probes to TH+ and TH-.

Test requires Ignition On.

CCDave

I missed this question.
My A340H auto trans is regularly shifting into O/D early (possibly slipping into O/D?) causing a temporary loss of power during acceleration. it also shifts into O'D even when O/D is OFF.
While going through the FSM steps to troubleshoot the transmission I came across the volt discrepancy with the temp sensor.