Code H15--
Thread Starter
Burning Brakes
Joined: Dec 2007
Posts: 1,068
Likes: 6
Code H15--
Got a situation here!
I replaced the water temp sensor on my '93 LT1 with no problem. I covered the opti with plastic, and a old towel over that, but in the end very little leaked out of the WP when I switched it out.
I had the new sensor at the ready, so it was a flawless swap!
Now, I'm getting a Check Engine light. I pull the code and it's a DTC 15 (Low temp indicated).
The temp on the guage is 142, even with a cold engine. The analog gauge work fine, however..
I took it for a spin to get it up to operating temp, and the digital readout stayed at 142, and the analog gauge worked properly. As soon as I started the car, the cooling fans came on (with a cold motor), and I don't recall that ever happening before.
I pulled the code again and sure enough, H15--again...
If the analog gauge is working properly, the sensor should be fine, correct? Or no?
Anyone have any suggestions/ideas/experienced this phenomenon before as well?
Thanks!
I replaced the water temp sensor on my '93 LT1 with no problem. I covered the opti with plastic, and a old towel over that, but in the end very little leaked out of the WP when I switched it out.
I had the new sensor at the ready, so it was a flawless swap!
Now, I'm getting a Check Engine light. I pull the code and it's a DTC 15 (Low temp indicated).
The temp on the guage is 142, even with a cold engine. The analog gauge work fine, however..
I took it for a spin to get it up to operating temp, and the digital readout stayed at 142, and the analog gauge worked properly. As soon as I started the car, the cooling fans came on (with a cold motor), and I don't recall that ever happening before.
I pulled the code again and sure enough, H15--again...
If the analog gauge is working properly, the sensor should be fine, correct? Or no?
Anyone have any suggestions/ideas/experienced this phenomenon before as well?
Thanks!
Melting Slicks
Joined: Dec 2004
Posts: 3,284
Likes: 51
From: Jacksonville, FL
St. Jude Donor '08 thru '26
Just a fwiw
I have a 90 so I don't know how much help these suggestions will be.:o
My motor has two temp sensors, one for the analogue gauge and another for the ECM.
Another friend had an issue with his A/C system, not exactly sure what the malfunction was caused by, but it was causing the ECM to think that the compressor was engaged and that turned on the fans all the time.
My motor has two temp sensors, one for the analogue gauge and another for the ECM.
Another friend had an issue with his A/C system, not exactly sure what the malfunction was caused by, but it was causing the ECM to think that the compressor was engaged and that turned on the fans all the time.
Safety Car
Joined: Jun 2006
Posts: 3,629
Likes: 28
From: FL
Got a situation here!
I replaced the water temp sensor on my '93 LT1 with no problem. I covered the opti with plastic, and a old towel over that, but in the end very little leaked out of the WP when I switched it out.
I had the new sensor at the ready, so it was a flawless swap!
Now, I'm getting a Check Engine light. I pull the code and it's a DTC 15 (Low temp indicated).
The temp on the guage is 142, even with a cold engine. The analog gauge work fine, however..
I took it for a spin to get it up to operating temp, and the digital readout stayed at 142, and the analog gauge worked properly. As soon as I started the car, the cooling fans came on (with a cold motor), and I don't recall that ever happening before.
I pulled the code again and sure enough, H15--again...
If the analog gauge is working properly, the sensor should be fine, correct? Or no?
Anyone have any suggestions/ideas/experienced this phenomenon before as well?
Thanks!
I replaced the water temp sensor on my '93 LT1 with no problem. I covered the opti with plastic, and a old towel over that, but in the end very little leaked out of the WP when I switched it out.
I had the new sensor at the ready, so it was a flawless swap!
Now, I'm getting a Check Engine light. I pull the code and it's a DTC 15 (Low temp indicated).
The temp on the guage is 142, even with a cold engine. The analog gauge work fine, however..
I took it for a spin to get it up to operating temp, and the digital readout stayed at 142, and the analog gauge worked properly. As soon as I started the car, the cooling fans came on (with a cold motor), and I don't recall that ever happening before.
I pulled the code again and sure enough, H15--again...
If the analog gauge is working properly, the sensor should be fine, correct? Or no?
Anyone have any suggestions/ideas/experienced this phenomenon before as well?
Thanks!
Thread Starter
Burning Brakes
Joined: Dec 2007
Posts: 1,068
Likes: 6
The analog gauge uses the sensor in the rt. cylinder head, the digital gauge uses the coolant sensor in the water pump that also supplies that information to the ECM. I would check the connector on the sensor you changed, if it is okay you may have gotten the wrong sensor. The fan is likely running because the DTC is in memory.
Now I remember seeing there were 2 sensors in the FSM. I've looked at so much information that it's all a blur at this point!
I cleared the codes, but the fan still turns on at ignition. I checked the sensor connection, and it looks ok. I had around 5v at the pigtail when I tested it with the multimeter, but I'm not really confident in that result. The 5v was recorded with the ignition switch in the 'off' position. The FSM states there should be 5 volts present, but I don't know if that was with ignition switch 'on' or 'off'. As you may deduct from my questions, I'm still a novice when it comes to electrical diagnosis...
Thanks!
Safety Car
Joined: Jun 2006
Posts: 3,629
Likes: 28
From: FL
Thanks,
Now I remember seeing there were 2 sensors in the FSM. I've looked at so much information that it's all a blur at this point!
I cleared the codes, but the fan still turns on at ignition. I checked the sensor connection, and it looks ok. I had around 5v at the pigtail when I tested it with the multimeter, but I'm not really confident in that result. The 5v was recorded with the ignition switch in the 'off' position. The FSM states there should be 5 volts present, but I don't know if that was with ignition switch 'on' or 'off'. As you may deduct from my questions, I'm still a novice when it comes to electrical diagnosis...
Thanks!
Now I remember seeing there were 2 sensors in the FSM. I've looked at so much information that it's all a blur at this point!
I cleared the codes, but the fan still turns on at ignition. I checked the sensor connection, and it looks ok. I had around 5v at the pigtail when I tested it with the multimeter, but I'm not really confident in that result. The 5v was recorded with the ignition switch in the 'off' position. The FSM states there should be 5 volts present, but I don't know if that was with ignition switch 'on' or 'off'. As you may deduct from my questions, I'm still a novice when it comes to electrical diagnosis...
Thanks!
Thread Starter
Burning Brakes
Joined: Dec 2007
Posts: 1,068
Likes: 6
I'm going to do that this afternoon when I get home. I'll let you know what happens!
Can I short them together using a paperclip?
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Safety Car
Joined: Jun 2006
Posts: 3,629
Likes: 28
From: FL
Tech 1 but I think the digital dash display should read the same with the wires shorted together.
Thread Starter
Burning Brakes
Joined: Dec 2007
Posts: 1,068
Likes: 6
Thanks! I was wondering what a Tech 1 was! I figured it was something expensive that I didn't have!
I do, however, have an abundance of paperclips, so all is well!
Thanks again for your help..
Safety Car
Joined: Jun 2006
Posts: 3,629
Likes: 28
From: FL
Do you have any type of scan tool or did you read the code using the paper clip technique?
Thread Starter
Burning Brakes
Joined: Dec 2007
Posts: 1,068
Likes: 6
The Tech 1 was the state of the art scan tool used in GM dealerships when these cars were built, long obsolete now. They can be found on E-bay sometimes very cheaply and can really help for some problems.
Do you have any type of scan tool or did you read the code using the paper clip technique?
Do you have any type of scan tool or did you read the code using the paper clip technique?
I used the paperclip method for retrieving codes on the speedo. I found an excellent writeup for it on another forum...
Thread Starter
Burning Brakes
Joined: Dec 2007
Posts: 1,068
Likes: 6
I checked temp on dash, pulled pig tail--No change 142
Jumped black and yellow on pigtail, no change...142
Jumped yellow to ground....you guessed it...no change
Multimeter on yellow to ground, key on....5 volts present..
Is this a bad ground wire perhaps? I've ordered a new sensor as well as new pigtail..
Safety Car
Joined: Jun 2006
Posts: 3,629
Likes: 28
From: FL
The black wire is the common ground for the temp sensor, TPS and oil temp sensor. To eliminate the ground side as the problem, ground the yellow wire directly to the engine and see if the temp reading goes to 266 with the key on.
Disregard that, after doing some checking this morning on my own car I must apologize for giving you some bad information. The ECM and digital display do both acquire the temp input from the sensor on the water pump but I led you astray saying the dash would give the same reading as the Tech 1.
Apparently the CCM takes the information from the ECM then sends it to the display only if it is within a certain range. When I disconnect my sensor guess what the dash displays? Yep, 142, but it also displays 142 with the sensor terminals shorted together or grounded to the engine just like yours.
You will need a scan tool that can read the sensor values from the ECM for the FSM tests to be valid, the dash display will not work. At this point I have to believe you got the wrong sensor or a bad one. I would ohm check the sensor and compare your reading to the chart in the FSM for DTC 15. PM me if you need a copy. Good luck, sorry for the error.
Disregard that, after doing some checking this morning on my own car I must apologize for giving you some bad information. The ECM and digital display do both acquire the temp input from the sensor on the water pump but I led you astray saying the dash would give the same reading as the Tech 1.
Apparently the CCM takes the information from the ECM then sends it to the display only if it is within a certain range. When I disconnect my sensor guess what the dash displays? Yep, 142, but it also displays 142 with the sensor terminals shorted together or grounded to the engine just like yours.
You will need a scan tool that can read the sensor values from the ECM for the FSM tests to be valid, the dash display will not work. At this point I have to believe you got the wrong sensor or a bad one. I would ohm check the sensor and compare your reading to the chart in the FSM for DTC 15. PM me if you need a copy. Good luck, sorry for the error.
Last edited by toptechx6; Mar 31, 2009 at 05:20 AM. Reason: updated information
Thread Starter
Burning Brakes
Joined: Dec 2007
Posts: 1,068
Likes: 6
The black wire is the common ground for the temp sensor, TPS and oil temp sensor. To eliminate the ground side as the problem, ground the yellow wire directly to the engine and see if the temp reading goes to 266 with the key on.
Disregard that, after doing some checking this morning on my own car I must apologize for giving you some bad information. The ECM and digital display do both acquire the temp input from the sensor on the water pump but I led you astray saying the dash would give the same reading as the Tech 1.
Apparently the CCM takes the information from the ECM then sends it to the display only if it is within a certain range. When I disconnect my sensor guess what the dash displays? Yep, 142, but it also displays 142 with the sensor terminals shorted together or grounded to the engine just like yours.
You will need a scan tool that can read the sensor values from the ECM for the FSM tests to be valid, the dash display will not work. At this point I have to believe you got the wrong sensor or a bad one. I would ohm check the sensor and compare your reading to the chart in the FSM for DTC 15. PM me if you need a copy. Good luck, sorry for the error.
Disregard that, after doing some checking this morning on my own car I must apologize for giving you some bad information. The ECM and digital display do both acquire the temp input from the sensor on the water pump but I led you astray saying the dash would give the same reading as the Tech 1.
Apparently the CCM takes the information from the ECM then sends it to the display only if it is within a certain range. When I disconnect my sensor guess what the dash displays? Yep, 142, but it also displays 142 with the sensor terminals shorted together or grounded to the engine just like yours.
You will need a scan tool that can read the sensor values from the ECM for the FSM tests to be valid, the dash display will not work. At this point I have to believe you got the wrong sensor or a bad one. I would ohm check the sensor and compare your reading to the chart in the FSM for DTC 15. PM me if you need a copy. Good luck, sorry for the error.
I've got a new sensor/pigtail ordered and will be here tomorrow. I'll check the ohm's on the new sensor prior to installaton, and check the old 'new' one as well for comparison.
Thanks again for taking the time to help me with this! Much Appreciated!
I'll let you know how it goes!
David
Safety Car
Joined: Jun 2006
Posts: 3,629
Likes: 28
From: FL
Thank you Sir! Man, no worries, I'm just relieved you got the same results as I did. All of this electrical diagnosis is new to me!
I've got a new sensor/pigtail ordered and will be here tomorrow. I'll check the ohm's on the new sensor prior to installaton, and check the old 'new' one as well for comparison.
Thanks again for taking the time to help me with this! Much Appreciated!
I'll let you know how it goes!
David
I've got a new sensor/pigtail ordered and will be here tomorrow. I'll check the ohm's on the new sensor prior to installaton, and check the old 'new' one as well for comparison.
Thanks again for taking the time to help me with this! Much Appreciated!
I'll let you know how it goes!
David
Please do David, I look forward to hearing the outcome.
Thread Starter
Burning Brakes
Joined: Dec 2007
Posts: 1,068
Likes: 6
UPDATE!
New coolant temperature Sensor arrived yesterday, and I got it installed last night!
Result: It's Fixed! No more code 15, no more SES light!
Guess I just got a 'dud' sensor the first time...
New coolant temperature Sensor arrived yesterday, and I got it installed last night!
Result: It's Fixed! No more code 15, no more SES light!
Guess I just got a 'dud' sensor the first time...
Safety Car
Joined: Jun 2006
Posts: 3,629
Likes: 28
From: FL
