Is the Enigine Coolant Temperature monitored by the PCM

[jhawkins]

I have 96 dodge ram 2500, 4x4, cummins 12v, auto transmission, and the PCM is showing an ECT high code, and the truck will not shifting into overdrive after it runs for a few minutes. I have checked all the usual stuff like TPS and the only thing I can find is this over temperature code.



The problem is the 96 engine only has one sensor, and the wiring diagram I got from Alldata does not show it is connected to the PCM. So is this code valid and if so does anyone have a wiring diagram that shows how the sensor is connected to the PCM?

Help

Jim

 

[Signal73]

try jumping the trans temp sender in the cooler line with a piece of wire to see if it makes the problem go away

 

[fest3er]

My '98 SM says the PCM will cause a downshift to D and lock up the TC if the temperature is too high (above 280F or so). Also, I don't remember exactly what the PCM does when the trans. is too cold; it might prevent TC lockup or it might prevent D-OD upshift. Basically, the PCM might be thinking the trans. is either too cold or too hot. It's prolly about time for it to be going through menopause anyway. I would expect the '96 to be kind-of similar. The following describes my '98; your '96 ought to be similar, but prolly won't be identical.

The sensor is a 'variable thermistor'; it resides in the trans. cooling line. It happens to have the same curve as the intake manifold air temp sensor (meaning the sensors are the same). High resistance (ohms) is low temp, low ohms is high temp. 50F-104F is about 20K ohms to 5. 4K ohms. 70F is about 12. 5K ohms; 80F is around 10. 1K ohms. All measurements are generally +/- 1K ohms. If the sensor is well outside this range, it should be replaced. Also check the wiring harness between the sensor and the PCM. If the resistance is > 1 ohm, it needs repair. You may have a 'transmission control module', which will site between the trans. and the PCM. ('May', because the 47RH has less electrical stuff than the 47RE. ) Hope this helps get you started on diagnosis.

 

[Missouri Mule]

Looking in my 96 service manual I don't see any thing that states the coolant temp sensor or temp gauge send any data to the PCM.



Some of the codes for the 96 t0 2001 code defintions apply to 98. 5 to 2001 trucks only (24 vavle engine which has a ECM).



What code are actually getting?

 

[jhawkins]

The code is P0118, ECT sensor voltage high. I do not recall ever getting this code before, but I really never had a problem like this before, so maybe it always was set. I was told by a transmission expert that this could cause the PCM not to signal the shift to 4th. So as nothing else seems to work I am trying this last possibility before I just give up and drive with my OD ground switch dangling from the cup holder, to manually shift it myself. It's kind of a pain in the ***. The thing is I cannot find any info on this code that says it is not valid for a 96 ,12v. Actually it's very hard to find any detailed information about the PCM so it's hard to tell if your wasting your time chasing a non problem. Thanks for the help. It's supposed to rain tonight so I do not know if I will get anything done tonight.

Jim

 

[San Felipe Bob]

96?

Maybe your 96 is a 97?

My 97 was built in late 96... .

Maybe your 96 was built in late 96 too?



try checking the build date on the door?



I'm having transmission lock up issues .....



Must be a transmission virus going around?

SFB

 

[jhawkins]

I looked at the build date on the door and it says it was built on 6 - 96. So I guess it is a 96.
Jim

 

[Missouri Mule]

From looking at my factory service manual the sensor only hooks up with the gauge. Mine was built in Jan. 96

 

[jhawkins]

From looking at my factory service manual the sensor only hooks up wiht the gauge. Mine was built in Jan. 96

Thanks, thats what I thought. If the 96 PCM does not monitor the coolant temperature wouldn't the engineers do something so the PCM want signal an error? It would seem they would change the program or do something to make it think everything is ok so the stupid PCM would not set a code. Especially if the code effects shifts. This is the origonal PCM and I have not had it flashed since the upgrades where made so something must have changed. Does anyone have a 96 with the P0118 ECT code?

Thanks

Jim

 

[Missouri Mule]

some reasons why trans mite not shift into overdrive:

1. Dash O/D switch in OFF position.

2. Overdrive circuit fuse blown.

3. Overdrive swttilch wire shorted/open cut.

4. Distance or Coolant sensor malfunction.

5. TPS malfuntion.

6. Neutral swtich to PCm wire shorted/cut.

7. PCM malfunction.

8. Overdrive solenoid shorted/open.

9. Solenoid feed orfice in valve body blocked.

10. Overdrive clutch failed.

11. Hydraulic pressure low.

12. Valve body valve stuck.

13. O/D piston incorrect spacer.

14. Overdrive piston seal failure.

15. Overdrive check valve/orrifice failed.



Apparently the service manual has two different scenarios for the coolant temp sensor/sender.



On page 8w-40 -6 it shows sending unit has no realtion with PCM but on 8w-30 4 under Engine coolant temp sensor it states the the coolant sensor sends data to the PCM. The wiring diagram on 8w-30-26 is for Gas Engine which relates to the coolant sensor interacting with the PCM.

 

[SLangone]

I currently have the code and do not know what to do.

 

[Gene Heck]

Just out of curiosity, is this a California spec truck? Does or did the the truck at one time have EGR on it? The California trucks monitors the coolant temp to work the EGR thru the PCM. They provide power to the sensor so it can report back as a PCM input. I think if you have this sensor it is mounted on the left side of the head kinda under the intake.



According to the 97 FSM, page 25-6, a P0118 is "ECT sensor voltage too high, engine coolant sensor input above maximum acceptable voltage". This is an emission control statement.





On a 49 state truck the sensor for the temp gauge on the instrument panel is on the left rear of the head and is not powered by the PCM.



Gene

 

[SLangone]

I think this truck has spent most of its time before I bought it in PA. I think I am just going to take it to the dealership and have them fix the issue for me.

 

[jhawkins]

I apologize for not posting that I fixed the shifting problem. As it turned out he crank angle sensor on the motor was bad. I had replaced it before all the shifting trouble started because the truck was not charging and the AC did not work. As I had just changed it, I just assumed it was OK, so I did not check it when the truck did not shift right. Anyway the part was not bought from Dodge and was just bad from the start. I think it was putting out a signal but it was not providing the PCM with the right speed so the truck would not shift into OD. I think the ECT fault is just a false code as everything I can find indicates the ECT is not monitored on a 2nd Gen 12V truck. I still have the code and everything works right so I am just going to ignore it. If you are not having a problem you should also.

 

[SLangone]

Well it could deal with a ground correct?

 

[jhawkins]

Is your temp gauge working? Does the dash gauge read between the first mark and the vertical mark? Can you see the reading changing after you start the truck and go for a drive? If so, the circuit is working fine. Only the newer trucks use this ECT sensor with the PCM. Mine only uses the sensor for the temp gauge on the dash. I had my transmission modified by MASSDIESEL and the PCM was reflashed after the upgrades. I think the new PCM program was for newer versions of the truck in which the PCM does check the ECT sensor. After the reflash my PCM started throwing the code. I never noticed it until the shifting problem occurred and I found the code when I checked the PCM. n my case this caused a lot of wasted time because I did not know the code was false. When I found the Crank angle sensor was bad and fixed it the shift problem went away. I changed the coolant temperature sensor earlier even though the dash temp gauge was working correctly because I thought the code was valid. It did not fix anything.

 

[SLangone]

I have not seen my gauge go above 140 or the first hash mark.

 

[jhawkins]

Does it move at all?

 

[SLangone]

Im not sure if it moves at all. Don't know what one looks like when it works.

 

[jhawkins]

The sensor is on the driver side of the engine near the fire wall. It's kind off difficult to get to. The sensor screws into the block and has a single wire going to it so I guess it uses the engine ground for an electrical return. When I changed mine, I removed the rubber seal at the top of firewall and then unscrewed the two relays that where in the way. I could then reach through the opening to replace the sensor. Basically you have to just lay on top of the motor to get to this thing. If that sounds like to much, you are probably better off just taking it in and having someone do it for you. Of course it could be a bad wire or connection somewhere so you might want to measure the resistance between the sensor's electrical connector and ground, to see if it reads within proper range before going to the trouble of changing it.