MadCleveland

Wondering if someone can tell me where this module is located. My ECT manual shows it is connected to my temp gauge. The temp gauge on my truck quit working. I've changed the temp gauge, the thermistor on the block and the gauge moves to the left when the ignition is turned on.

Thanks.

cts2433

The Emission Maintenance Warning "EMW" module is located bottom of instrument panel and left of steering column. The EMW operates a light that is located on the instrument panel. For 1988-89 model year vehicles, the light will display the words "CHECK ENGINE". When the light is lit, it is indicating that the 60,000 mile emission maintenance should be performed. After the maintenance is performed the EMW module must be reset to zero time. Another type of module is the "IMS" module. This module is not part of the light circuit and does not require maintenance. At a predetermined time, the IMS module directs the EEC IV processor to make a strategy change. A third type of module is the "COMBO" module. This is the one you have. This module combines the functions of the IMS and the EMW modules, however, this had no bearing on your temperature gauge.


As far as the coolant temp gauge, it seems that you have eliminated everything except the wiring. You probably have either high resistance or an open circuit on the sender wire (common issue on the 8th gen). Also double check the printed circuit on the back of the cluster where the connector plugs in, as I've seen the ribbons slip out of position. Did you replace the single wire temp sender? Unplug and ground the sender wire and turn the ignition on. The needle should sweep to hot (coolant temp sender resistance is 74 ohms cold and 10 ohms hot).

MadCleveland

Thanks for your post. Very helpful. Yes, I replaced the single wire temp sender as well as the double wire coolant sensor just to be thorough. I've grounded the sender wire and the needle sweeps to hot as it should (shouldn't this mean the sender wire is not open?). I have not pulled the panel. I went as far as removing the gauge but did not go further.

Thanks, what is the 8th gen?

?

cts2433

Sounds as if you either have a bad/incorrect coolant temp sender, coolant level low, or possibly a poor engine ground.

MadCleveland

Oddly, the coolant temp sensor that was removed tested correctly with leads attached to an ohm meter when it was dipped into boiling water. The coolant has been changed and replaced with 50/50 mix.

As for the engine ground, doesn't the circuit go to ground at the temp sensor in the block?

Thanks. If I had any hair I'd pull it out.

cts2433

Yes, the temp sender grounds through the engine, assuming you have a good engine ground. I would check continuity between negative battery terminal to temp sender. If high or open circuit then check your engine grounds - The engine ground strap grounds to wiper motor stud. The negative battery cable attaches to stud on front right of engine and the cable also has an inline wiring eyelet that is bolted to crossmember (behind carbon canister). If all okay then I would pull cluster and ohm check sender wire between sender and cluster.

MadCleveland

Thank you very much. I won't be able to work on the truck until the weekend, but will let you know how things work out. I'm grateful for your assistance.

MadCleveland

Passed continuity test between thermistor and negative battery cable (disconnected from battery). Next check will be at instrument cluster.

If the gauge moves to Hot with ignition on, engine off when sensor line is grounded, the manual says the gauge is functioning properly.

ECT Manual shows a two hot lines to gauge, one from the Engine Trouble Module and the other from the power feed to the instrument panel, which ultimately goes to ground after passing across temp gauge. The line from the Engine Trouble Module is shown as proceeding to ground at the thermistor.

So, if the needles goes hot when thermistor line is grounded, doesn't that mean the line is good and that the problem lies ahead of the gauge or in the feeds to the gauge from the instrument panel or the Engine Trouble Module?

MadCleveland

Looks like a bad circuit board. Ribbon on board is broken in the area behind the temp gauge. Looks like the engine warnng indicator module is a printed semiconductor board that connects to the circuit board on the instrument cluster frame behind the temp gauge.

Found a new board on ebay and it will arrive in a weeks time.

MadCleveland

Replaced circuit board to correct broken ribbon. Problem persists. Gauge goes left when ignition turned on, and does not register temperature.

The gauge itself has three prongs. Should I be getting 12V across instrument? Way out of may league here.