One more question please. Do I need an ECU?

[msnewman]

I have been chasing bugs in this car for over a month now. When I bought the car it had a bad transmission (imagine that) and had been sitting for 2+ years. The guy pulled the transmission out. It looked like he unplugged the engine and transmission plugs with a screwdriver and pliers, busted them all. He also cut the engine control wiring harness where there were 30 or so wires. This created a wiring nightmare. I have been through every electrical connection and wire on this thing correcting and clearing all the codes and I finally got this thing running right. Except for one thing ….
When I start the car (cold start) I have no CEL. As the car warms up to about half way on the gauge (“R” in the word NORMAL) the CEL comes on. I pull the code and it’s 9. I have changed both temp sensors. (2 pin sensor for the ECU and the single pin for the gauge). I have checked the actual temperature of both radiator hoses (175°) and the radiator. Just before the CEL comes on I can hear a click (fan relays I think) and both fans come on full speed. I have tested the fan relays and they are good. If I am correct the fans (or at least 1 on them) are 2 speed fans. I can pull the relays next to the under the hood fuse box and slow the passenger side fan down. I think only one fan should come on when the temperature gets to normal operating temperature. The second fan should not come on unless the AC or Defrost is on or the coolant it actually HOT. It seems that the ECU calls for one fan, sees an error, and defaults to running both fans full speed. Kind of like a non responding HO2 sensor will trigger the ECU to default to a preset fuel/air mixture. This is with the all accessories OFF including the AC and Defrost. I am out of things to check/test. Any advice?

[KevinD]

Fan operation.
This is for a '93, but later years work the same, simply substitute the ECT for the ECTF Sensor.
Have you checked your coolant level?
Have you double checked the ECT Sensor wiring all the way back to the PCM?
KevinD

[msnewman]

Have you checked your coolant level?

Yes I have checked the coolant level. Is there a coolant level sensor?

Have you double checked the ECT Sensor wiring all the way back to the PCM?

Yes I have checked the wiring.

simply substitute the ECT for the ECTF Sensor.

ECT = Single wire temperature sensor? Gauge sensor?

ECTF = Two wire temperature sensor? PCM sensor?

The 2 wire sensor (ECTF) has a 5 volt input and a vairable output that increases on temperature rise. How can I substitute it for a single thermocouple output?

Thanks for the schmatic information Kevin. Now I know how is should work and I can check/test it.

Also, It's my understanding that the '93 only has one temperature sensor so there can only be one temperature input to the PCM. How many temperature inputs to the PCM are on the '94 and up?

[KevinD]

simply substitute the ECT for the ECTF Sensor.

I meant to do this for the document...

ECT = Single wire temperature sensor? Gauge sensor?

The single-wire sensor is the gauge sensor, not the ECT.

Also, It's my understanding that the '93 only has one temperature sensor so there can only be one temperature input to the PCM. How many temperature inputs to the PCM are on the '94 and up?

You've got it backwards: the '93 has two coolant temperature sensors: the ECT Sensor near the centerline of the motor (beside the gauge sensor) sends signals to the PCM for engine temperature, and the ECTF sensor in the coolant elbow sends signals to the PCM for fan control. '94+ uses the ECT sensor only for engine temperature & fan control (there is no ECTF sensor).
KevinD

[msnewman]

Now I am very confused! This car has 2 temperature sensors. Both sensors are near the centerline of the engine beside each other (as you described). A 2 pin sensor that has 5 volts suppling it and a single wire sensor. If I unplug the 2 wire sensor both cooling fans come on even if the car is cold. If I unplug the single wire sensor the temp gauge drops to nothing.
The car is a 1994 Ford Probe GT according to the title and door plate. The engine VIN matches the car VIN as the engine that came in the car.
You sure about the '94 and up only having 1 sensor? Ya'll know more that me buy I remember reading post about people putting a 93 engine in newer modles and asking what to do about the second temp sensor that they have a plug for but no hole to screw it in. One person drilled and tapped a hole into the coolant neck for his '96 after installing a '93 engine.

[cry0m0nkey]

Now I am very confused! This car has 2 temperature sensors. Both sensors are near the centerline of the engine beside each other (as you described). A 2 pin sensor that has 5 volts suppling it and a single wire sensor. If I unplug the 2 wire sensor both cooling fans come on even if the car is cold. If I unplug the single wire sensor the temp gauge drops to nothing.
The car is a 1994 Ford Probe GT according to the title and door plate. The engine VIN matches the car VIN as the engine that came in the car.
You sure about the '94 and up only having 1 sensor? Ya'll know more that me buy I remember reading post about people putting a 93 engine in newer modles and asking what to do about the second temp sensor that they have a plug for but no hole to screw it in. One person drilled and tapped a hole into the coolant neck for his '96 after installing a '93 engine.

why didnt you say it was a 94 in the first place and that you were putting a 93 engine into it, that is way more helpfull! but I dont know the answer to this one lol.

[KevinD]

Apparently I made an erroneous assumption in that you'd be able to use the document I posted to assist the troubleshooting of your problem.
IGNORE the ECTF: your '94 DOES NOT HAVE or USE an ECTF.
If you still have a code 09, then the ECT Sensor or circuit still has a problem. If you've verified the circuit, and are ABSOLUTELY CERTAIN that you've a correct, functional ECT sensor, then the PCM is about all that's left in the circuit.

KevinD

[neilh2o]

it is very unlikely you have a failure in the PCM....The Engine Coolant Temperature (ECT) sensor detects the coolant temperature, and constantly updates the Powertrain Control Module (PCM) on the coolant's changing condition with an input signal. The PCM uses this signal to modify ignition timing, EGR flow (1.3L and 2.5L), air/fuel ratio, idle speed, and purge flow.......................measure the resistance of the ECT sensor... at 68 degrees F the resistance of the ECT sensor should be 2.2-2.5k ohms...at 176 degrees F the resistance decreases to 250-350 ohms...the ohm values at slightly higher or lower temps should be fairly close in value to the above factory ECT sensor specs...make sure you have the right sensor.. check that your thermostat is opening at around 180...double check the two relays wiring into the PCM (one is for the hi speed fan, one for the lo speed)..the PCM monitors coolant temp, vehicle speed and air conditioning status to determine when the fan operation is required..if the condenser fan runs all the time with the AC and defroster turned off its most likely that one of the two relays has its N.O. contacts stuck closed...try tapping on both relays to free up the contacts..if that doesnt work replace the relays..theres also an AC relay..if that relays contacts are stuck closed you would have both fans turning on

[msnewman]

OK, I checked the ohms at the ECT to make sure that the sensor is working. I connected the meter to the ECT and drove the car. The temperature gauge (I know the gauge uses a separate sensor) leveled out at the “M” in NORMAL and the ohms were 211. This is where the car normally runs and this is where both fans come on full blast and the CEL comes on.

I pulled the low and high speed cooling fan relays and the condenser fan relays out of the car and tested them using a 12 volt power supply. Both relays worked correctly. Appling power to the coil switched the NO contacts to closed and the NC contacts to open.
The low speed relay contacts are fed through a NC set of contacts off the high speed relay, so when the high speed relay energizes the power to the low speed relay contacts is lost. I wired the relays this way based on the link KevinD posted.
I did the same test on the condenser fan relays. They also worked perfectly.

Does the PCM ever turn on both fans based on an engine temperature input or does turning on the AC and/or the defroster the only thing that will trigger the condenser fan to run?

And KevinD, there is no mention of an ECTF or an ECT in the document you linked. I just assumed you were talking about the two temperature sensors for the PCM and the gauge that are on my ‘94. Thanks for the link. I used it to simulate the PCM output. Now I can rule out the relays as the problem and maybe the ECT although 211 ohms may be a little low.