Faulty Water Temp Sensor - Causing Problems?

The code means the coolant temp sensor circuit is either open or shorted. Could be as simple as a bad connection, but most likely the sensor is bad. You can test it with an ohmmeter.

Check the factory manual, ENGINE - MFI SYSTEM - ECT SENSOR section. If you don't have an fsm, google 1993 toyota pickup service manual.

The ECT is one of many sensors on an aluminum appendage ("coolant block") on the top of the motor in the back - just in front of the firewall and half under the plenum. The 93 collection of sensors is slightly different than the 90, but the position of the ECT is the same. The ECT is on the driver's side, in the back row. There's another sensor a little further left, but that one is in the forward row: you don't want that one. If you get the new ECT first, you'll be able to positively identify the old one, because fortunately all the sensors on that block look different.

If the ECT is bad, it must be replaced in order for the motor to run right. Be careful when you order it to call it by its right name: engine coolant temp sensor (ECT). There's a coolant temperature sender too (for the gauge) and you don't want that one. The naming of them does vary in the catalogs of various parts suppliers, but USUALLY the ECT is called a sensor and the temp gauge sender is called a sender. They look different: the ECT has a plastic connector on top:



...and the gauge sender just has a metal tab:



The other way to know the difference is the price: the ECT costs $20-40 more than the sender.

Safest bet is a sensor from Toyota - 1sttoyotaparts.com probably has the best price, but it will still be more than aftermarket. Half the time, I can't find the part I'm looking for in their catalog, so I just call them and ask for the internet parts sales guy (forget his name, but he knows his stuff).

Autohausaz.com sells an ECT that is probably Japanese-made and could well be the same part the dealer sells - cost is $51. They call it the "Water Temp. Sensor" and it's in the Fuel Injection section of their catalog. They also sell an o-ring for it but the o-ring may come with the sensor - ask them.

The cheapest ECT I would take a chance on would be the Beck/Arnley from rockauto.com. They want $31 for it. Many of the B/A parts for our cars come from Japanese manufacturers, but not all. At $31, this one probably isn't Japanese-made. Rock Auto calls it the "Coolant Temperature Sensor" and it's in the Cooling System section. Both AutoHausAZ and Rock Auto are excellent, trustworthy vendors - I've bought parts from both of them many times.

If it were me, if the dealer part from 1sttoyotaparts was too much $$, I'd pony up for the NTC from autohausaz.

While you're helping your buddy with sensors, when is the last time he replaced the oxygen sensor? If it's over 90k miles old, it also needs to be replaced - over time it gets coated with carbon and starts to read leaner than the exhaust really is. As a result, the computer runs the motor too rich. The computer has no way to know if the readings of the O2 sensor are inaccurate - it only knows if the sensor fails completely or if it is really, really bad.

Sparkplugs.com sells Denso's (the best bet) at a good price, and NGK's (if $$ is tight). You can also get the Denso part number from the sparkplugs catalog and search for it on Amazon - I got myself a brand-spankin new Denso for just over $50 that way.

Good luck.

Thank you for all the great info! That's good to hear. Hopefully that will fix his problem. I'll check the sensor with an ohmmeter (I take it I'm just looking for an open circuit in the sensor...not a specified resistance range correct?).

I just happen to live close to the dealership that runs 1sttoyotaparts.com so I can order it and pick it up (done that a few times for some parts). I did do some searching and the only part on the website that had "water" and "sensor" in it was a part called: "Air intake temp sensor, pick-up, land cruiser, van, water temperature" for $50.50...is that the right one? Kind of an odd part name...I'll have to give them a call to be sure.

So let me get this straight...there are two water temperature sensors? One for the gauge and one for the computer? That's good to know...don't want to end up replacing the wrong one.

Good call on the O2 sensor. He's had the truck for 50k miles and has never replaced it...I'm sure the sensor is way over its expected lifetime.

Thanks again for the help! I'll report back with our progress :thumbsup:

Can someone with a service manual for a 1990 4runner (V6) verify that this is the correct chart for checking the ECT?



I found it online but it said it was for a '95. Would they be the same?

Thanks

Here's an update:

I removed his sensor yesterday to check it with my multimeter. It tested within the correct range after I initially pulled it out, so it wasn't looking good for finding out the problem. To be sure, I took it inside and stuck it in hot water and took a reading. Nothing. Put it in the freezer and still couldn't get a reading. After it sat around for a while I was able to get a reading off it until I warmed it up again. So thats good! Bad sensor. We picked up a new one and I performed the same tests on both sensors one more time to be sure. Anways, so that is one problem fixed.

I cleared the computer of codes and then we started it up. When it was sitting there idling, I tried giving it a little gas. You could increase the revs fine if you go easy on the throttle, but if you punched it at all the revs would drop way down and the engine would want to die out...it would recover though after a few seconds. Well crap I didn't know what to think. But as soon as the thermostat opened up (I could see the temp gage go right up to temp), the revs dropped down to the normal idle. I tried giving it some gas again and it had perfectly fine throttle response. No dying out or anything.

So it seems that the motor only ran crappy when it was in open loop mode. I told him to let it sit and start it up cold this morning to see if it did the same thing. I haven't talked to him yet. Since this was the initial startup after it ran bad before, could that have anything to do with it? I thought maybe it was a computer problem still trying to recover from the last problem...I dunno.

But we got the sensor fixed for sure, hopefully that will get him back on the road for a little while.

Thanks for all the help.

PS. What is the temperature sensor that is next to the ECT? I accidently pulled that one out first because it has the same exact plug as the ECT but the threads were bigger and the temperature probe is larger. It doesn't look like the temp sender because of the plug. I was just curious to what it is. (it registered around 80 ohms at the outside temp).

Congrats on getting the sensor replaced, and thanks for posting the outcome.

The stumbling that happens when the motor is cold and the throttle is opened very quickly is something my engine has always done. I've checked everything, and I think it's just a shortcoming of the ecu's programming when in open loop. Apparently the later years don't do that, so I can only guess that they got the ecu dialed in a little better after a few years. On mine, it's no problem if I'm gentle on the throttle, and it's no problem after a few minutes when the motor reaches operating temp.

You might check the tps and vafm, and check for vacuum leaks, and make sure the throttle body is clean and the plugs, wires, cap, rotor & air filter are good, and timing is set correctly. That should probably be done anyway, but if the motor acts like my 89, it will still stumble when the throttle is opened too quickly when in open loop.

I forget which sensor (other than the obviously different and smaller temp gauge sender) is next to the ECT - could it be the cold start injector time switch??