Code 15 with new sensor - Defender Source
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Old June 4th, 2012, 02:09 PM
slowpoke496
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Bryan
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Code 15 with new sensor

I have been chasing a strange problem or combination of problems. First is intermittent engine kill. my 94 V8 D-90 would just turn off as if i turned the key off. Engine, dash lights, and everything else would just go off. replaced the electrical portion of the ignition switch and it went away except for one re-occurrence... might have a short in the dash somewhere...

the second more troubling is erratic idle after the truck is warm. replaced stepper control, PCV hoses, speed sensor, coolant sensor, fuel filter, fuel pump, I have a mallory dizzy and good spark. Connected to rovergauge and drove the truck after replacing everything and the idle now seems to be okay. not perfect but i remember that after disconnecting battery it takes time for the ECU to reach an equilibrium.

Now rovergauge and the code readout agree that code 15 fuel temperature sensor is not functioning. replaced it with a brand new sensor and went through clearing the codes and the code comes right back. I have double confirmed that i did not switch coolant and fuel connections.

I am going to go for a longer test drive today but i am wondering if anyone has had an issue clearing the fuel temp sensor code or knows of a reason for a false code 15?

PS rovergauge is pretty cool
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  #2  
Old June 4th, 2012, 09:55 PM
slowpoke496
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After 10 minutes at idle in drive way ECU threw an intermittent coolant temp code. replaced sensor and drove for 30+ minutes with no issues. still have code 15 fuel temp sensor code and confirmed with Rover Gauge that there is now signal. reads -48 F.

Since it is a brand new fuel temp sensor I installed a spare ECU and there was no change.

Does anyone know what the sensor (fuel) should be outputting?
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Old June 5th, 2012, 07:28 AM
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leastonce
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Quote:
Originally Posted by slowpoke496
After 10 minutes at idle in drive way ECU threw an intermittent coolant temp code. replaced sensor and drove for 30+ minutes with no issues. still have code 15 fuel temp sensor code and confirmed with Rover Gauge that there is now signal. reads -48 F.

Since it is a brand new fuel temp sensor I installed a spare ECU and there was no change.

Does anyone know what the sensor (fuel) should be outputting?
Sounds like a bad connection to me ... But this will help you do some diagnosis.

If you disconnect the sensor completely what value do you get?

My understanding is that default values get inserted if the sensor is missing.

http://p38arover.com/rover/p38a/Engi...UX_Systems.pdf
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Old June 5th, 2012, 11:28 PM
slowpoke496
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Bryan
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LeastOnce thanks for link. I disconnected the sensor and the reading remained at -48F.
I found the table below and will check the sensor tomorrow. I believe it is good and like you said it is a bad connection somewhere between the sensor and the ECU. I might connect the sensor right next to the ecu with a temporary connection to see if it can get a good reading.

Correct reading-Temperature to
resistance
- Proceed to Test 13(Refer to Temperature Conversion Chart below.
Fuel and Coolant Ohm-meter Reading
Temperature Should be
C F Ohms
-10 14 9100 - 9300
0 32 5700 - 5900
20 68 2400 - 2600
40 104 1100 - 1300
60 140 500 - 700
80 176 300 - 400
100 212 150 - 200
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Old June 6th, 2012, 07:36 AM
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leastonce
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Jason England
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Quote:
Originally Posted by slowpoke496
LeastOnce thanks for link. I disconnected the sensor and the reading remained at -48F.
I found the table below and will check the sensor tomorrow. I believe it is good and like you said it is a bad connection somewhere between the sensor and the ECU. I might connect the sensor right next to the ecu with a temporary connection to see if it can get a good reading.

Correct reading-Temperature to
resistance
- Proceed to Test 13(Refer to Temperature Conversion Chart below.
Fuel and Coolant Ohm-meter Reading
Temperature Should be
“C “F Ohms
-10 14 9100 - 9300
0 32 5700 - 5900
20 68 2400 - 2600
40 104 1100 - 1300
60 140 500 - 700
80 176 300 - 400
100 212 150 - 200

Sounds like you've probably damaged a wire somewhere or have a bad connection .... On the scale above a very high resistance or broken connection would result In a very low temp reading ... Just like you are seeing. Have you done any work on your truck where you have disconnected any plugs ( may not be properly seated ) or cut anything?
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Old June 6th, 2012, 11:07 PM
slowpoke496
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Bryan
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It seems the PO had modified the wiring to the fuel temp sensor and did a terrible job making sure that the crimp connectors would not touch.... Every time i disconnect the plug from the sensor to check for shorted or broken connection the crimp connectors would separate and everything would appear normal. When the cable was reconnected they would touch again. fixed the short and potted it in epoxy to prevent them touching.
too late to go for a test drive but the code is cleared and will test it tomorrow.

thanks for the help!
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