DIY Coolant Temperature Sensor change (PICS)
12-31-22, 08:00 PM
#301
Lexus Champion
What are the the things that suggest that? The thermostat isn't stuck open or closed because that would be obvious? What suggests thermostat over CTS. Or does this symptom list also suggest a sluggishly responding, but otherwise correct thermostat, which causes the car to stay in cold-start for longer, but will otherwise not overheat or over-cool.
12-31-22, 08:11 PM
#302
T+10 minutes took the picture (below)
...
T+17 minute the car (finally) hit normal operating temperature as indicated by the needle
I'll remove the picture since it's confusing. The temp gauge reaches the correct reading. The car does not run cold, it will reach the correct operating temperature. Hydraulic fan clutch was replaced a few years back as well - OEM, it functions correctly. My heat does not blow cold indicating stuck-open thermostat.
Last edited by 400fanboy; 12-31-22 at 08:15 PM.
12-31-22, 08:26 PM
#303
Lexus Champion
After re-reading your post I think you are on the right track, engine ECU temp sensor is not working correctly.
12-31-22, 08:28 PM
#304
Yeah sorry - the picture was misleading if you missed the one important line describing it within my long essay lol.
Thanks!
Thanks!
12-31-22, 08:31 PM
#305
Moderator
What are the the things that suggest that? The thermostat isn't stuck open or closed because that would be obvious? What suggests thermostat over CTS. Or does this symptom list also suggest a sluggishly responding, but otherwise correct thermostat, which causes the car to stay in cold-start for longer, but will otherwise not overheat or over-cool.
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LeX2K (12-31-22)
01-03-23, 07:01 PM
#306
The plot deepens... I hooked the car up to a scan tool and measured the fuel trims and reported engine coolant temperature.
When the car was stone cold, the reported coolant temp was accurate to within 2 degrees of ambient. Ambient was 4 degree Celsius, the sensor reported 6 degrees Celsius. Once I turned the car on, it then climbed linearly at a degree every 10 seconds as the car warmed up. There were no jumps or spikes.
After 10 minutes, with the exhaust still smelling like fuel, the fuel trims were all over the place. Bank 1 is identical to bank 2. As the engine warmed up, short term started at negative 7 and continued to get worse reaching a peak value of -13%. And the long-term trim started at zero and got up to about +7.
But then one minute later once it crossed over 70 degrees and no audible or other discernable change to the engine the trims invert and reset. The exhaust stopped smelling like fuel.
There was no further fuel trim change after this. The engine coolant stabilized at 80c which is right on the money for a 180 degree fahrenheit thermostat. Fuel trims stayed 0% short term and -5% long-term, which makes sense to me considering I'm at 5000ft elevation.
This... doesn't feel like the coolant temp sensor to me anymore. As far as I can tell the coolant temp appears to be accurate. This appears to be normal operation of the cold-start process... but a process which takes a really, really long time. And a process where the exhaust smells incredibly fuel rich in the process, which is confirmed by my abysmal fuel economy on short trips.
Thoughts? Thanks.
When the car was stone cold, the reported coolant temp was accurate to within 2 degrees of ambient. Ambient was 4 degree Celsius, the sensor reported 6 degrees Celsius. Once I turned the car on, it then climbed linearly at a degree every 10 seconds as the car warmed up. There were no jumps or spikes.
After 10 minutes, with the exhaust still smelling like fuel, the fuel trims were all over the place. Bank 1 is identical to bank 2. As the engine warmed up, short term started at negative 7 and continued to get worse reaching a peak value of -13%. And the long-term trim started at zero and got up to about +7.
But then one minute later once it crossed over 70 degrees and no audible or other discernable change to the engine the trims invert and reset. The exhaust stopped smelling like fuel.
There was no further fuel trim change after this. The engine coolant stabilized at 80c which is right on the money for a 180 degree fahrenheit thermostat. Fuel trims stayed 0% short term and -5% long-term, which makes sense to me considering I'm at 5000ft elevation.
This... doesn't feel like the coolant temp sensor to me anymore. As far as I can tell the coolant temp appears to be accurate. This appears to be normal operation of the cold-start process... but a process which takes a really, really long time. And a process where the exhaust smells incredibly fuel rich in the process, which is confirmed by my abysmal fuel economy on short trips.
Thoughts? Thanks.
Last edited by 400fanboy; 01-03-23 at 09:02 PM.
01-13-23, 12:52 PM
#307
Coolant temp sensor is fine. I did not replace, nor do the tests Yamae suggested (I don't have the equipment sorry!). But I did what I could which involved the following: monitoring coolant temp while sticking a thermometer in the air vents. Coolant temp sensor reported correct ambient temp when car was off. And the air coming out of the vents was never hotter than the reported engine coolant temp as the car warmed up. If the air coming out of the vents, from the heater core, were hotter than the reported engine temp that would suggest the coolant temp sensors is sluggish\sticky\wrong. The engine temp rose linearly and it's rate of growth increased when I applied throttle (more heat). Full operating temp is spot on the money with out 180 degree thermostat, right at 84c. My guess is the coolant temp sensor appears to be functioning correctly and shouldn't cause the issues I'm experiencing (rich exhaust and terrible fuel economy while car is cold, with no CEL).
My testing has moved to other components (O2 sensors) for my particular problem. Depending on how successful I am at figuring this out, I may just leave it be and not replace the sensors considering how expensive they are. However, I worry is the extended lifetime spent with fuel rich cold start may damage the cats. So we'll see.
I haven't repaired my ECU, but at the moment I don't suspect it.
My testing has moved to other components (O2 sensors) for my particular problem. Depending on how successful I am at figuring this out, I may just leave it be and not replace the sensors considering how expensive they are. However, I worry is the extended lifetime spent with fuel rich cold start may damage the cats. So we'll see.
I haven't repaired my ECU, but at the moment I don't suspect it.
Last edited by 400fanboy; 01-14-23 at 12:48 AM.
06-25-23, 08:01 AM
#308
little help please
this threads over a decade old now so wont be surprised if no one replies but I was just wondering if anyone has replaced these sensors to fix a no start issue? I have a 97' Ls400 that cranks turns over then cuts fuel and wont throw anymore engine codes I already checked out these sensors and they are both in need of replacement so they're already on the way in the mail just wondering if anyone here has been in my shoes before
06-25-23, 12:40 PM
#309
If it's completely failed or reporting wildly inaccurate numbers, yes, it may cause a no-start.
06-25-23, 12:49 PM
#310
I believe the electrical connections to both have been completely broken so essentially like they’ve been completely disconnected, gonna try throwing on new connectors to the OEM parts
06-25-23, 01:37 PM
#311
Moderator
The cam and crank sensors are 2 obvious examples. I don't remember the others off the top of my head. Maybe someone else can chime in to confirm..?
I don't think the ECT sensor is part of this group.
Last edited by bradland; 06-25-23 at 03:15 PM.
06-25-23, 08:24 PM
#312
My limited understanding is a faulty\disconnected coolant temp sensor may cause the ECU to start the engine on the wrong fuel map, causing a rich\lean condition and no-start.
02-06-24, 12:00 PM
#313
9th Gear
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UPDATE 09/05/08 - 69 degrees in Indianapolis today with relative high humidity (it rained earlier).
I am still blown away by the vast difference this simple sensor has made to the driving characteristics of my car.
I've done a few simple 0-60 mph runs with a digital stopwatch and figured I'd have a go at it again today.
Nothing scientific, not perfect, not a dragstrip timing system, just my finger on the button hitting start when I release the brake and stop when I see 60mph on the speedo.
In the beginning, my LS always felt somewhat slower than it should be. Using the same test, same road it did like 8.2 - 8.1 seconds to 60mph.
At its worst, I saw a 10.2 second 0-60 about a month ago.
Today, same road, same non scientific approach: Brake torque to 1,500 rpm -- traction control off, ETC on, manually shifting the 1-2 at 6,200rpm, it registered a 7.53 0-60 run.
End Update:
_____________________________
After reading this thread:
https://www.clublexus.com/forums/sho...d.php?t=376713
I decided to give it a try myself. I have noticed a slight decrease in gas mileage as well as a significant sporadic decrease in performance. Right now in Indiana it is about 92 degrees and humid, so... the weather has some to do with it, but I found the thread interesting nevertheless.
The entire procedure was quite basic, but because of the different covers on the 1UZ it took some time to get to the sensor.
I spent about 2 hours from start to finish.
1. A generic 1995 1UZFE in my Lexus with 72k miles on the clock. New plugs and wires about two months ago.
Attachment 439746
2. I started by just removing the upper manifold cover with the three 10mm bolts, but found that the coolant temperature sensor is hidden under the front spark plug wire channel.
Attachment 439747
3. It is located directly under the spark plug wire channel. This needs to come out and the spark plugs need to be carefully pulled out of the way.
Attachment 439748
4. So... I decided to just pull all of the plastic parts off of the engine. This included the intake pipe, two spark plug covers and the front spark plug wire channel. These all come off with 10mm sockets. I also went ahead and removed the front coil pack with a screw driver and disconnected the weather fitting. It gave me more clearance.
The coil pack is connected to a metal bracket with 4 screws. The bracket is then connected to another bracket with 2 10mm screws. I removed the bracket for better clearance.
Attachment 439749
5. And here it is... One OEM Toyota Coolant Temperature sensor. It is the larger green colored sensor. It was removed with a 3/4" (I didn't have the metric equivalent) deep socket.
Attachment 439750
6. Here is the new aftermarket coolant temperature sensor that I bought from autozone for $29.00 plus tax. It comes with its own copper washer. I installed this sensor with the same 3/4" deep socket and torqued it down very slowly until it was snug. Remember this is aluminum so be careful.
Attachment 439751
7. After that, the parts all go back on in reverse order. I pulled the ECU fuse as well as the negative battery terminal and waited about 10 - 15 minutes while I put my tools away before taking her for a drive.
Note - I did this on a slightly warm engine and zero coolant leaked out or spewed out of the hole once I removed the sensor.
Conclusion:
This was very simple and not time consuming. I noticed right away a significant increase in throttle response as well as a smoother power delivery across the entire range.
I run BP or Shell 93 in the tank and while I know it was still 92 degrees outside, I am looking forward to seeing what some cooler temperatures do to the car both performance and gas mileage.
Best,
Dustin
I am still blown away by the vast difference this simple sensor has made to the driving characteristics of my car.
I've done a few simple 0-60 mph runs with a digital stopwatch and figured I'd have a go at it again today.
Nothing scientific, not perfect, not a dragstrip timing system, just my finger on the button hitting start when I release the brake and stop when I see 60mph on the speedo.
In the beginning, my LS always felt somewhat slower than it should be. Using the same test, same road it did like 8.2 - 8.1 seconds to 60mph.
At its worst, I saw a 10.2 second 0-60 about a month ago.
Today, same road, same non scientific approach: Brake torque to 1,500 rpm -- traction control off, ETC on, manually shifting the 1-2 at 6,200rpm, it registered a 7.53 0-60 run.
End Update:
_____________________________
After reading this thread:
https://www.clublexus.com/forums/sho...d.php?t=376713
I decided to give it a try myself. I have noticed a slight decrease in gas mileage as well as a significant sporadic decrease in performance. Right now in Indiana it is about 92 degrees and humid, so... the weather has some to do with it, but I found the thread interesting nevertheless.
The entire procedure was quite basic, but because of the different covers on the 1UZ it took some time to get to the sensor.
I spent about 2 hours from start to finish.
1. A generic 1995 1UZFE in my Lexus with 72k miles on the clock. New plugs and wires about two months ago.
Attachment 439746
2. I started by just removing the upper manifold cover with the three 10mm bolts, but found that the coolant temperature sensor is hidden under the front spark plug wire channel.
Attachment 439747
3. It is located directly under the spark plug wire channel. This needs to come out and the spark plugs need to be carefully pulled out of the way.
Attachment 439748
4. So... I decided to just pull all of the plastic parts off of the engine. This included the intake pipe, two spark plug covers and the front spark plug wire channel. These all come off with 10mm sockets. I also went ahead and removed the front coil pack with a screw driver and disconnected the weather fitting. It gave me more clearance.
The coil pack is connected to a metal bracket with 4 screws. The bracket is then connected to another bracket with 2 10mm screws. I removed the bracket for better clearance.
Attachment 439749
5. And here it is... One OEM Toyota Coolant Temperature sensor. It is the larger green colored sensor. It was removed with a 3/4" (I didn't have the metric equivalent) deep socket.
Attachment 439750
6. Here is the new aftermarket coolant temperature sensor that I bought from autozone for $29.00 plus tax. It comes with its own copper washer. I installed this sensor with the same 3/4" deep socket and torqued it down very slowly until it was snug. Remember this is aluminum so be careful.
Attachment 439751
7. After that, the parts all go back on in reverse order. I pulled the ECU fuse as well as the negative battery terminal and waited about 10 - 15 minutes while I put my tools away before taking her for a drive.
Note - I did this on a slightly warm engine and zero coolant leaked out or spewed out of the hole once I removed the sensor.
Conclusion:
This was very simple and not time consuming. I noticed right away a significant increase in throttle response as well as a smoother power delivery across the entire range.
I run BP or Shell 93 in the tank and while I know it was still 92 degrees outside, I am looking forward to seeing what some cooler temperatures do to the car both performance and gas mileage.
Best,
Dustin
Hi dustin having the same problem with the engine coolant temperature sensor I was getting good mileage and when I changed it mileage went horrible just wanted to know your thoughts
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