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1994 B2300 2.3L - Fault Code 118

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Old 03-01-2019
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1994 B2300 2.3L - Fault Code 118

I am getting this code 118 (engine coolant temp sensor above max voltage / 0 to -40F) intermittently on my 1994 B2300 2.3L. Replaced coolant temperature sensor, thought it would take care the problem but fault code came back. Some guy mentioned online that 118 = ECT sensor circuit open (possible broken wire)?? With KOEO, measured 5 volts across the sensor. wiggled wires to the sensor and no drops on voltage, so wires to sensor is good. I live in south CA, outside temperature never drops below 50F during this time. Please advise.
 

Last edited by B2300Truck; 03-01-2019 at 11:23 PM.
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Old 03-02-2019
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ECT sensor should have 5v on one wire and then 3v down to .5v on the other wire

Use a sewing needle to pierce the light green/red stripe wire and test voltage, this wire runs to Pin 7 on the computer
Cold engine outside temp of 70deg should show about 3volts
After engine is warmed up, say 170deg, you should see about .75volt, under 1 volt

Computer expects to see under 1 volt after 10minutes of running, if not it can set 118 code, could mean thermostat is stuck open, so engine is not warming up fully
Does the dash temp gauge work?
And is it showing engine is fully warming up, same as it did before?
Gauge uses a Sender so not related to the ECT sensor


If you want to test old ECT sensor in hot water, OHMS(and voltage) seen here: https://www.explorerforum.com/forums...hms-gif.79355/
 
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Old 03-02-2019
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Thanks for the info.

ECT sensor has one 5V wire and the other one is ground (I believe).

The temperature gauge is working and I noticed that the gauge points lower than before when engine is fully warming up. I think that my thermostat is stuck open or no good. I am planning to change out the thermostat since it's quite cheap and not hard to do.

I have tested the old ECT sensor in hot water, the result matches with the chart you provided. So it's good.
 

Last edited by B2300Truck; 03-02-2019 at 01:53 PM.
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Yes, signal return is a Reference Ground and may or may not test as 0 ohms to an engine ground, it is a grey/red stripe wire in most years and it runs to pretty much every sensor, O2 uses Orange wires spliced to grey/red wire

And except for the O2, sensors will reference .1 to 5volts as the "feed back", the voltage is what computer uses to "read" the sensor

If engine has been running cooler you should have seen a lower MPG, won't be much but you may have noticed it
The correct thermostat will be 190 to 195degF, don't used 180degF
And it should have a "jiggle" valve, that IS the technical name, lol, small hole in the t-state plate with a loose fitting metal pin in it
Jiggle valve should be placed at 12:00 position
Its purpose is to let air out as you refill with coolant, or anytime air might get into the system.

Remember to Swap heater hose locations at the firewall any time you work on cooling system, it reverses flow thru core and will extend its life
 
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Old 03-02-2019
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Ron, is there any write-up online about your statement - "Computer expects to see under 1 volt after 10 minutes of running, if not it can set 118 code"
 
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Its in the software so a bit hard to follow

But this article talks about it: https://www.underhoodservice.com/dia...ature-sensors/

Its geared more to the EEC-V so OBD2 codes, but P0125 and P0128 are similar to the older EEC-IV OBD1 3 digit code 118

If the indicated ECT data hasn’t reached the -desired operating temperature during a specific time limit and at a specific engine speed and load factor, the PCM might set a P0125 (insufficient temperature for closed-loop operation) or a P0128 (coolant temperature below thermostat-regulated temperature), which in most (but not all) cases -indicates a bad thermostat. If this diagnostic strategy sounds complicated, that’s because it is complicated, and also because it can vary widely among different applications.
 
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Old 03-02-2019
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Ron, one last question for you. When installing the new thermostat with outlet gasket, do I still put RTV silicone around it?
 
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I do, thermostat housings are usually not all that flat, especially when older.
RTV also helps hold gasket in place during assembly
In other words, it can only help and won't hurt :)
 
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Old 03-04-2019
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Update:

I connected a voltmeter to monitor the ECT sensor while driving locally. From cold start to fully warm-up was about 10 mins. Voltage started at 3.5V and went under 1.0V after 4 mins, and dropped to 0.6V after 10mins, then it flipped between 0.6V and 0.7V afterward.

Per you chart, 0.6V = 194F and 0.7V = 185F.

It looks like everything was working correctly and no fault code 118 detected during this test.

Please advise.
 
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Old 03-04-2019
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A thermostat uses "wax" to detect temperatures, lol, yes wax is still what they use
And a thermostat is a moving part, albeit a slowly moving part it is still mechanical

So maybe it stuck open for a few drive cycles, you did say dash temp gauge looked lower a few times?

Thermostats are suppose to "fail safe", that means when they wear out they should stay open, failing in a safe way so engine doesn't over heat, this, of course, doesn't always happen, lol.
But yours could be near "end of life", but just guessing
 
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Old 03-04-2019
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The dash temp gauge looks little lower than before. I am not even sure if the thermostat has a "fail safe" feature because it was changed out 7 years ago by some shop. They replaced the water pump at the same time. This time around, I will replace upper/bottom hoses, thermostat, and water pump myself. It is pretty cheap as far as parts go.
 
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Update: Fault code 118 has never come back after securing the wires on the temperature sensor. Thanks for all the support.
 

Last edited by B2300Truck; 1 Week Ago at 09:21 PM.
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Good work

Thanks for the update
 
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