Checking resistance and voltage on the ECT sensor

First check for codes. Failure in either the circuit or temperature sensor will show code 21, 51, 61 or 116, 117, 118.

• Unplug the harness connector.

• 
  First, check the signal voltage at the connector with the key on, engine off. Should be approximately 5.0v.

• Then, check the resistance of the sensor cold. Should be between 58,750 to 40,500 ohms.

• Plug in the harness connector and warm up the engine to normal operating temperature.

• Then, unplug and check the resistance of the sensor hot. Should be 3,600 to 1,840 ohms.

The Haynes Manual outlines testing for all sensors.

You can also compare your values against a nifty chart like this:



Remember, when backprobing for voltage, turn the ignition key on. For resistance tests, turn the key off.

Seattle FSB said:

First check for codes. Failure in either the circuit or temperature sensor will show code 21, 51, 61 or 116, 117, 118.

• Unplug the harness connector.

• 
  First, check the signal voltage at the connector with the key on, engine off. Should be approximately 5.0v.

• Then, check the resistance of the sensor cold. Should be between 58,750 to 40,500 ohms.

• Plug in the harness connector and warm up the engine to normal operating temperature.

• Then, unplug and check the resistance of the sensor hot. Should be 3,600 to 1,840 ohms.

The Haynes Manual outlines testing for all sensors.

Click to expand...

SeattleFSB, Thanks for the information. I can do almost all of that. The one thing that I have put in bold print is the main culprit. I can go by the gauge inside for warmup, but, I am not sure if it actually warmed up. The idle stays at the same RPM's (650-700) from cold start up to when "warm". We have rechecked the timing, it is at 13 TDC. Should I have it at 10 TDC for all troubleshooting?




When I first completed my MAF upgrade. I got DTC 118. But, with only repinning a new harness and installing my fender mount remote IDM, as well as repositioning my spark plug wires, when I run codes, it is gone?

Doesn't make sense to me. Truck still doesn't know when it is cold, so it doesn't have the "warming up" stage with the higher RPM's to then return to normal idle. Temp gauge seems to work just like before in the rig. Gets hot, thermostat opens up, temp level goes down.

Codes had been run KOEO and KOER time and time again. Only code still is DTC 136. HOS2 sensor always lean. O2's have been replaced with new 1995 O2's. I am going to check volts and resistance on both of my connections today. I hope I am not confused, but, I thought I read some where that if the ECT is bad or anything, it will cause the PCM to "think" the motor is warm and at normal working temp.

I have replaced all my green , red , yellow lines with straight up vacuum lines. The truck will still sometimes lope and stall at idle.

I have a few tests that still need to be done. Got some other personal shit going on so, I haven't been able to get to it. But today, I should be able to.

It also hit my that I forgot to mention that I have antifreeze coming from between I think what is the timing cover and block. I saw it first on the right hand side coming down the block, at first I thought it was coming from between my block and heads. I don't think so now because I have two nice puddles on each side of the the timing cover. I topped off my radiator before I started up the rig after my MAF upgrade. That is when I got the DTC 116 code. I don't know if that has anything to do with my ECT, unless it is rusted out now? I am digging into this problem today.

I also hope to be able to:

Test the fuel Pressure.

Test the MSD Coil. I think it has been on there for about 3-4 years? I am not sure how long they last. But, that has been a thought as to being a culprit for a bit. Just didn't "think" it would be.

I do apologize and appreciate your guy's patience and tolerance with me. I am so freaked to start it up because I am afraid of me messing the motor up. I can in no way afford to rebuild another motor. LOL , Meaning my Bronco would sit, and that would just kill me. LOL. Kills me now looking at the ol' sob in the driveway, while I jump into a friggin minivan to work. LOL. Guess you don't know what ya got until it's gone.

I know one thing. When and if I ever to put another motor in. It will be a straight up stock 351w. LOL. Maybe just a cylinder bore and headers. that is it. LOL

I have checked the voltage on my ECT connector. It is 4.62 volts

My ECT cold is at 22.00 ohms? I am not sure what this means?

I have a pic of it below. Am I testing it incorrectly?

Weird. 22kΩ indicates about 90°F, according to the chart. I mean, that's not THAT far off really. :scratchhe The PCM only has a resolution of ±2°F, so...yeesh.

This is why I like using voltage tests, instead of resistance, whenever I'm troubleshooting. I know: theoretically, it shouldn't make a difference, but the PCM measures and interprets voltage, not resistances. It also helps eliminate other sources of problems like connectors, wiring, and other flakiness.

However, if you'd like to test its resistance again, I'd advise testing it at more than a single temperature. Throw it in your freezer for a while and measure, then submerge it in hot (~180°F) water and measure again.

Just for fun, here's the transfer function that's actually programmed into the PCM. It's not prettied-up for diagnostic purposes (although my voltage scaling is probably a very small bit off).

yo,

Go thru this too;
Engine Coolant Concerns TSB 93-24-08 for 84-94 Bronco, F Series, Aerostar, Econoline & many others; "...ISSUE: Engine performance concerns such as hesitation or stall, rough idle, and/or poor fuel economy may be caused by the thermostat stuck in an open position or opening at a temperature lower than specified. ACTION: Use the following "Cooling System Diagnosis" procedure to diagnose a cooling system that may not be reaching normal operating temperature

by Ford via Steve83 (Steve, That dirty old truck) at http://www.supermotors.net/registry/media/723355



TSB 93-24-08 Engine Coolant Concerns

Publication Date: NOVEMBER 24, 1993

FORD: 1983-94 ESCORT
1984-87 EXP
1984-94 CROWN VICTORIA, MUSTANG, TEMPO, THUNDERBIRD
1986-94 TAURUS
LINCOLN-MERCURY: 1984-86 CAPRI
1984-87 LYNX
1984-92 MARK VII
1984-94 CONTINENTAL, COUGAR, GRAND MARQUIS, TOPAZ, TOWN CAR
1986-94 SABLE
1988-89 TRACER
1991-94 CAPRI, TRACER
MERKUR: 1985-89 XR4TI
1988-89 SCORPIO
LIGHT TRUCK: 1984-94 BRONCO, ECONOLINE, F-150-350 SERIES, RANGER
1985-90 BRONCO II
1986-94 AEROSTAR
1988-94 F SUPER DUTY
1991-94 EXPLORER
MEDIUM/HEAVY TRUCK: 1993-94 F & B SERIES
NOTE: THE ESCORT/TRACER SPECIFIC APPLICATION FOR THIS ARTICLE IS AS FOLLOWS:
1983-1990 Escort - 1.9L and 1.6L
1991-1994 Escort - 1.9L
1991-1994 Tracer - 1.9L Only

ISSUE: Engine performance concerns such as hesitation or stall, rough idle, and/or poor fuel economy may be caused by the thermostat stuck in an open position or opening at a temperature lower than specified.

ACTION: Use the following "Cooling System Diagnosis" procedure to diagnose a cooling system that may not be reaching normal operating temperature. Follow the "Thermostat Diagnosis" procedure to determine if the thermostat may be at fault. Check the thermostat without removing it from the vehicle by using Rotunda Service Coolant Temperature Monitor Harness 007-00064.

DIAGNOSIS PROCEDURE
A new cooling system diagnosis procedure has been developed for engines that do not reach normal operating temperature. A new thermostat diagnosis procedure also has been developed, using a new service coolant temperature monitor harness. See chart for proper diagnostic procedure.

NOTE: THIS PROCEDURE WILL DIAGNOSE ONLY COOLING SYSTEMS THAT MAY NOT BE REACHING NORMAL OPERATING TEMPERATURE. IT WILL NOT DIAGNOSE A THERMOSTAT THAT CAUSES AN ENGINE OVERHEAT CONDITION.

THERMOSTAT DIAGNOSIS
NOTE: DISCONNECTING THE POWERTRAIN CONTROL MODULE (PCM) TO ATTACH A BREAKOUT BOX OR AN EEC IV MONITOR WILL ERASE THE ADAPTIVE LEARNING FROM MEMORY AND MAY "HIDE" A DRIVE CONCERN TEMPORARILY UNTIL THE ADAPTIVE LEARNING IS RE-LEARNED.

NOTE: THIS PROCEDURE IS MOST ACCURATE IF PERFORMED INDOORS AT LESS THAN 100°F (38°C) AMBIENT TEMPERATURE. THIS TEST MAY BE PERFORMED WITH OR WITHOUT THE HOOD OPEN AND WITH THE ENGINE WARM OR COLD.

CAUTION: ALWAYS VENT THE EXHAUST TO THE OUTSIDE WHEN PERFORMING THIS TEST.

1. Check the coolant level in the radiator and coolant recovery reservoir.
2. With the key in the "off" position, proceed as follows:
a. Remove the engine coolant temperature (ECT) sensor harness connector.
b. Attach Rotunda Service Coolant Temperature Monitor Harness 007-00064 as a jumper between the PCM and the ECT.
c. Attach Rotunda 73 Digital Multimeter 105-00051 or equivalent to the thermostat monitor harness. Voltage values (0-5vdc) may now be monitored while the sensor retains its connection to the wiring harness.
NOTE: A ROTUNDA NEW GENERATION STAR TESTER (NGS) 007-00500 OR THE ROTUNDA SERVICE BAY DIAGNOSTIC SYSTEM (SBDS) 001-00001 MAY BE USED TO MONITOR THE ECT ON VEHICLES EQUIPPED WITH DATA COMMUNICATIONS LINK (DCL). THE SBDS SEQUENCE TO USE FOR THE SCREEN IS "TOOLBOX - ELECTRONIC ENGINE CONTROL AND DCL - ITEM".
3. Vehicles equipped with electric engine cooling fan(s) must have a fan running during this test (high or low speed may be used). Two methods may be used to turn the fan(s) on:
a. Disconnect the A/C compressor clutch power supply and turn the climate control to A/C "ON". Or
b. Disconnect the power supply to the cooling fan and supply 12 volts direct to the fan connector from the battery.
NOTE: A GROUND MAY BE REQUIRED FOR SOME APPLICATIONS.
4. Place transmission in "park" or "neutral".
NOTE: RUNNING THIS TEST WITH THE VEHICLE IN GEAR OR WITH THE A/C COMPRESSOR CLUTCH ENGAGED (RUNNING) WILL CAUSE IMPROPER DIAGNOSIS
5. Start the engine and allow to idle throughout this test:
a. Allow engine to run for 2 minutes, then record ECT voltage.
b. From now on, record ECT voltage every 60 seconds.
c. When the ECT voltage trend changes direction or changes only slightly (0.03 volts or less) from the previous reading, record this as the thermostat opening voltage.
d. Use the "Voltage and Corresponding Temperature Chart" shown below to obtain actual coolant temperatures.
6. If the opening voltage is GREATER than 0.75 volts (less than 180° F/ 82° C), or 0.85 volts (170° F/ 77° C) for 2.3L HSC engine only, replace the thermostat. Refer to the dealer Master Parts Catalog for correct thermostat usage.
7. If the thermostat opening voltage is LESS than 0.75 volts (greater than 180° F/ 82° C), or 0.85 volts (170° F/ 77° C) for 2.3L HSC engine only, the thermostat is good and should NOT be replaced. The "Cooling System Diagnosis Chart" should be referenced for further instructions.
NOTE: The 10° F opening temperature difference for the 2.3L HSC engine is due to the ECT sensor location.

OTHER APPLICABLE ARTICLES: NONE
SUPERSEDES: 93-14-04
WARRANTY STATUS: INFORMATION ONLY

UPDATE

Been a while, But, still need some help from the folk who know a hell of a lot more then I do on this stuff.


I replaced my ECT on a whim, Bought a Motocraft. RockAuto.com is THE best site ever. Thanks Sig!:thumbup

Fixed my warm up issue I believe. THe idle actually raised up when cold and mellowed when warm.

I only still threw one code. That DTC 136.

The only thing left to do is check Fuel Pressure and my coil.

I know the fuel pumps whine a little, but, mine is singing pretty... Guess I will find out after the Fuel Pressure test, which, hopefully I can do this week.

First, I would replace the thermostat. There is an excellent chance this is why the engine is not warming up.

Regarding the ECT, this is a "Sensor" that gives input to the computer to assist is determining timing advance and air/fuel ratio. It has nothing to do with the gauge.

The Temp Gauge is controlled by a Temp "Sender" which has a single wire. To test, turn the key on, unplug to "Sender" and ground the single wire. If the gauge goes full tilt, it is good.