Jeep 4.0L Coolant Temperature Sensor Replacement

Today I noticed that my Jeep was having another idle issue. The RPM were slow to come down to idle. When letting off the accelerator with clutch pushed in or in neutral the RPM would come down to 1000 RPM then go back up to 1100-1200 then return to a normal 700RPM. It had also begun to run rich. I checked for codes (using the CEL) and it gave the codes for "Coolant temp too low" & "Temp sensor circuit fail". I replaced the temp sensor (for the computer not the gauge) and it's running normal again. I guess the bad temp sensor was keeping it from switching over to closed loop mode for the fuel injection. Running it in open loop caused it to run rich and caused the RPM issue since the PCM thought the engine was not warm yet.

[@zxtenn]

I have a 96 ZJ 5.2 and the OBD was telling me the coolant temp sensor was bad, also once in a while the check eng. light would come on= code 0138. I did some reading and found that running in open loop too long and too rich would trip the light due to engine not fully heating up quickly enough from faulty coolant sensor. I replaced the sensor and also the O2 with a Bosch unit and it's 100% with engine running at higher normal temp, also getting better heat--

[@jeepcollector91]

I would start off with cleaning the idle air control valve. I have had the same symptoms you mention happen several times since I have owned the '91 YJ and cleaning the IAC will usually eliminate the issue for many years. Every time it happens on the '91 I am expecting cleaning not to work again and figured I would have to replace it but it keeps working. The temp sensor issue was also causing problems with idle but mainly slow to return to idle. IAC caused start up idle issues.

[@bleepinjeep]

sweet vid

[@jeepcollector91]

No, you don't have to drain the coolant since not much will be lost as long as the radiator cap is left on. As for you're recurring problem, I would guess wiring or connector issue but it is possible to have obtained a faulty "new" sensor.

[@jeepcollector91]

My YJ gave code #17 "Engine Running Too Cool" and code #22 "Coolant Temperature Sensor or Circuit Fault". Its nice that the YJ ('91-'95) will give out the codes with the check engine light. No tools or scanners required.

[@revolutionday1]

Simple, plain, and to the damn point. No g00fy monologues about past divorces etc. or trying to sell t-shirts, like a lot of these other clowns making these type of videos. Thank you for that! Was it not necessary to bleed any air out after filling up, or you just didn't take the level down low enough to warrant it?

[@jeepcollector91]

Changing this temp sensor I didn't drain the coolant much lower than the level at the sensor. What little air ended up in the system was quickly worked out by simply squeezing the upper radiator hose a few times during and after topping off the coolant. Even when draining the system entirely I haven't had any air trapped in the 4.0L that required anything more than the simple hose squeeze. Hope this helps. Thanks!

[@revolutionday1]

@@jeepcollector91 You a Led Zeppelin fan? "....squeeze my hose, baby.....'till the coolant runs down my leg" :-D

[@jeepcollector91]

I always try to "Just Expect Every Problem" so I don't have to "Just Empty Every Pocket"

[@aarondmtz2178]

In my '97 Wrangler TJ - recently got a check engine light with a P0118 code. The Temp Gauge was steady reading and not bouncing around so I replaced the coolant temp sensor on the thermostat housing. Should I have replaced the one on the engine block towards the back of the head too? Thanks!

[@liberty2774]

My Temperature gauge sets at the middle mark between 100 and 210, can someone tell me which one is bad, is it the temperature sender or the temperature sensor? Any help would be great, thanks!

[@toddgreathouse6742]

Its the sensor on the bbacck of th head

[@Giovani25x]

Are all cooling temperature sensors all the same ?? I have a yj 1991 to wrangler to 4.0 .

[@jeepcollector91]

Yours should be the same as the in this video. It is a 1991 Jeep Wrangler YJ Sahara with the 4.0L

[@jeepcollector91]

On the 4.0L '91-'96 its on the top of the head on the drivers side (left side) all the way at the rear with just one wire plugged onto it. Hope this helps. Sorry I did not show that in the video. If changing that sensor doesn't fix your gauge issue you might want to make sure it's not the gauge itself.

[@jeepcollector91]

My YJ doesn't have an electric fan, just the mechanical fan. Been a while since I messed with an older XJ. Are you saying it stays on all the time, or wont turn on? Could be any of the following: A/C switch, bad relay, wiring issue, temp sensor. Might search on JeepForum or NAXJA

[@Aceknight22]

Thank you so much! Excellent Quality Video!

[@jeepcollector91]

Glad I could help. Thanks.

[@nickcastagno2841]

I have a 91 also how can I see what codes it's throwing for the check engine light to be on

[@jeepcollector91]

Turn the key from *OFF* to *ON* 3 times (not to start) and on that 3rd time leave it *ON* and within seconds the check engine light will flash out the codes for you. Then you can look the codes up in your schematic or simply Google them. Most of the Jeep forums will have them listed as well as some of the Jeep parts sites...

[@jeepcollector91]

I did a quick search. Here is a link to a good video and they even listed the codes in the description. kzbin.info/www/bejne/oaardq2FhqynhdU Hope that helps.

[@j3sis]

it only comes on when i switch from air cond. to heat but only stays on for about 5 seconds. it blew a small fuse under hood several months ago and made brakes lock up and ran hot and turned check anit lock light on but after fuse change it does this now so idk just trying different things bc its not a big issue bc its cold outside now so yeah

[@jamieclendenin7332]

this video is great! i have 7engine codes! from TPS sensor to Crankshaft sensor, EVAP code, fan relay codes! messed round with pcm wire harness and some basic cleaning! it has helped, BUT when the fan kicked on to cool engine, engine light came on and jeep again spuutter putt putt. ole betsey fired back up and after fan shut off it ran normal! every time fan kicks on jeep goes crazy! she shuts off when driving, red lights, idle! but no overheating so if you guys have any ideas, let me know please!

[@jeepcollector91]

+Jamie Clendenin Electric fan? If so, could be the wiring to the fan shorting against other wires in the harness and only showing itself when power is being sent down that wire. Just a thought.

[@MrElcochito]

is necessary drain the coolant for replace the sensor? because i replaced the sensor but i didn't drain the coolant..and the computer show the same problem( bad coolant sensor) thanks for your help.

[@azeezazeez8963]

M8

[@Cjansen087]

As funny as this is about to sound I know its the sensor. I just read up that sensors for idiot lights and gauges are different. I had idiot lights and I am in the process of changing over to gauges. Thanks for your advice. []||||[]

[@Cjansen087]

Too bad you didn't show where the other one was. My gauge isn't reading right and I have no idea where the sensor is for it.

[@j3sis]

i have a 92 cherokee 4.0 and im having trouble with the aux fan cutting on and i was wondering if this could be a bad coolant temp sensor

[@murkydiver]

awesome my friend...I am having the same problem on mine....you saved me a trip to the dealer to search for error codes... LOL Love my 91 YJ! Thanks for the tip!

[@jamieclendenin7332]

good thought!! im going to get that part today and i will get back with you. ty for the advice!

[@ryanmulle6963]

I did the same thing and even bough the rear temp sensor for it. However, the engine light still throws a code for faulty temp sensor unit...but they are both new. Maybe pig tail it bad?

[@jeepcollector91]

I don't think the rear temp sensor will cause any codes so I would focus on the wiring for the front temp sensor. Maybe even check the wiring connector for the computer since corrosion on the terminals could be part of the issue. Worst case, it could be the computer itself but lets hope for a simple broken or corroded wire and/or connector.

[@jeepcollector91]

...also, could be that the replacement sensor is faulty. Highly unlikely but still a possibility.

[@rigmo8]

It is called a sender, not sensor.sensor is the one on the back of the head.sender talks to the ECM ,sensor talks to the gauge.

[@jeepcollector91]

+m bnam Also known as the coolant temperature sending unit...

[@TheZoogTV]

Assbackwards! The gauge uses a sender. The ECM uses a sensor. Just like the video host states.

[@Hollywoodhouse74]

m bnam temp. Sending unit send to the dash gauge, the sensor sends it to the ecm..

[@sabbr92275656]

You can clean it by sanfra paper

[@jeepcollector91]

It was $20.99 at Advance Auto Parts.

[@jeepcollector91]

I believe there is only one on your '98.

[@almac828]

Will the location of the temp sensor be in the same spot on a 1997 jeep grand cherokee limited 4,0?

[@jeffmaser5817]

I have a 98 Jeep Cherokee Sport 4.0 l engine. Temperature gauge is erratic. When the temp. needle on gauge drops, the motor starts to ping when accelerating. It will then rise to normal position and pinging goes away. The gauge keeps going up & down, and always pings when it drops. Is this the temp. sensor causing this?

[@jeepcollector91]

I doubt the temp sensor is your issue. Maybe PCM, harness, or other electrical issue.

[@pitoreyes6960]

You may have air inside the engine cooling system. Follow these steps. 1. With engine cool, remove radiator cap. 2. Start engine. 3. Add coolant into radiator as needed and put cap back again. If the problem is solved after follow these steps, you don't have a sensor problem but maybe a leak of coolant somewhere.

[@leftoverfish12]

Can that sensor cause the motor to over heat? And I know it's not part of this video but if the hose connecting to the thermostat housing gets hard does that mean the thermostat isn't opening up?

[@jeepcollector91]

Ruben Cancino No, the temp sensor shown in this video shouldn't cause an overheating issue. It just causes the computer to get false readings making the engine run rough. Overheating issue could be a bad thermostat, water pump, clogged up water passages in the engine or radiator, bad fan clutch, and even something as simple as airflow obstructions on the face of the radiator (mud, bugs, leaves...) If the hose is staying hard with pressure and the temp gauge around 180 or higher then yes the T-stat could be faulty. You can remove the thermostat and test it in a pot of water on the stove with a thermometer to see what temp it's opening and to determine if that is the primary cause of the overheating issue. Even if you replace it with a new one I would say test the old one so you know you are actually fixing the problem and not throwing parts at it... Hope this helps.

[@jeepcollector91]

thanks.

[@eclipsedandjaded]

You're a life saver, I just encountered this problem today.

[@04passatgls]

jeep= Just Expect Every Problem

[@sunbear76re]

I've changed the temperature sensor, and the sensor on the back of the engine, also checked fuses, and have a new radiator and new water pump, and my jeep is still over heating, also my fan won't turn on, I've tested and gave it power and it works good, reason why I changed the temperature sensor to begin with. any ideas? some say the jeep shouldn't over heat with out it, I have a 1996 jeep cherokee 4.0 2wd straight 6, runs at 210 buy it's tipping to 250 almost.

[@jeepcollector91]

Been awhile since I messed with an XJ. Doesn't that electric fan mainly come on with the A/C? Anyway, if your XJ still has the mechanical fan you could have a faulty fan clutch which is less than $40. Assuming you already changed the thermostat? If that isn't the problem then it could be a number of other things. Anything from blocked coolant passages in the block, to compression issues in the cooling system. Sorry I'm not much help.

[@sunbear76re]

+JeepCollector91 year right now as we speak I'm using a oms reader tracing back the wires of the fan, but I asked my dad if it could be the fan clutch and he said no, super lost,the relay is good, I took the starter relay off and took the fan relay and put it where the starter one gos and cranked right up... maybe I'll find a break with the wire

[@uploader8297]

Wonder if you figured this out. I had the same problem, changed the thermostat, problem solved.

[@sunbear76re]

+Up Loader changed it also. front and back sensors, and the one in water pump. new fan clutch also. still a mystery. last thing is getting a fan shroud. I did not have one for a year or two and ran good. all in all I rewired the second electric fan to a switch in side the jeep. temp fix. still runs a little too warm. last thing to do is rewire the whole jeep and new fuse box that sits near the engine.

[@tacodirt9533]

Does anyone know a part number or replacement for the connector? Need to replace the pigtail on a '91 YJ and cannot find a compatible connector.

[@jeepcollector91]

I'm pretty sure it is this one with the rounded corners. www.oreillyauto.com/detail/b/standard-ignition-5753/lighting---electrical-16777/connectors-sockets-16631/coolant-temperature-sensor-connector-11457/e39bbaf30c53/standard-ignition-2-terminal-multi-purpose-connector/tx3a/5826087

[@poopoogang]

You said there was 2..where is the other one located?

[@jeepcollector91]

On 4.0L engines with head casting number 7120 the sensor for the temp gauge is on the top of the head near the rear, next to the valve cover on the same side as the exhaust/intake.

[@poopoogang]

Ahhhhh got you. thanks

[@jeepcollector91]

...no problem

[@mattatat1138]

So how bad is it if you crack the place the temp sensor goes into? Fml.

[@jeepcollector91]

***** If you are saying you cracked the thermostat housing it isn't too much of a problem. You can usually buy one off ebay or at your local U-Pull salvage yard for about $5. Then just buy a new gasket and install the replacement housing. Could replace the thermostat while you have it removed.

[@livinglargeandfree8322]

O'Reilly had one for my 95xj it was 15$

[@revolutionday1]

$7 (plus shipping), for a brand-new part, with a new gasket, on RockAuto.com, people!!

[@jeepcollector91]

Yes, same place.

[@rexlive1]

my jeep wj won't start the 1st crank or sometimes the 2nd when it's hot I have to wait for it to cool down then start it up. check engine light says it could be low coolant or senor I replace both ... help please!

[@jeepcollector91]

+rexlive1 It will turn over but not start correct? Assuming you have the 4.0L. I don't think your temp sensor issue is related to the hot start issue. That would cause more of a slow start issue meaning you just have to turn it over a little longer than normal to get it to start or just cause it to run rough or rich. Have you checked for spark when hot? I remember a few TJ's and some later XJ's were having issues with the coils on the coil on plug 4.0L's. Never messed with a WJ. Could also check the crank position sensor and maybe even the cam position sensor which took the place of the distributor on those later 4.0L's.

[@jeepcollector91]

...also, you could ask some of the WJ owners over on JeepForum

[@rexlive1]

+JeepCollector91 thanks for your help. I will try these and I will let you know if it helped BTW I have been to 3 mechanics but they couldn't help my cursed jeep wj :(

[@rexlive1]

+Travis Patocka got the changed no difference also nessed up the timing on it

[@rexlive1]

+Travis Patocka turned out it was my FUEL Filter , changed it 2 times its running fine now :)