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2nd Gen Ram Tech 1994-2001 Rams: This section is for TECHNICAL discussions only, that involve the 1994 through 2001 Rams. For any non-tech discussions, please direct your attention to the "General discussion/NON-tech" sub sections.

p0118-ENGINE COOLANT TEMPERATURE SENSOR HIGH

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Old 12-27-2011, 08:16 PM
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Default p0118-ENGINE COOLANT TEMPERATURE SENSOR HIGH

Just got warning p0118 after doing a bunch of work.

I found threads on p0117 but that is for the same code but "low".

Do I just need to replace the sensor by the thermostat?
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Old 12-27-2011, 10:21 PM
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Just found this

The engine coolant temperature (ECT) sensor is a variable resistor, that measures the temperature of the engine coolant. The powertrain control module (PCM) supplies 5 volts to the ECT signal circuit and a ground for the ECT low reference circuit.

When the ECT is cold, the sensor resistance is high. When the ECT increases, the sensor resistance decreases. With high sensor resistance, the PCM detects a high voltage on the ECT signal circuit. With lower sensor resistance, the PCM detects a lower voltage on the ECT signal circuit. If the PCM detects an excessively low ECT signal voltage, which is a high temperature indication, DTC P0117 sets.

If the PCM detects an excessively high ECT signal voltage, which is a low temperature indication, DTC P0118 sets.


Looks like its all points to the ect, I will replace that.
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Old 12-27-2011, 10:33 PM
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Do you know what the engine temperature actually is when this occurs? One of my other trucks says engine too cool when it is at 195. Really crazy. If you knew waht temp was it may save changing a part that may not be bad. At least you would know for sure first.
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Old 12-27-2011, 10:53 PM
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The gauge in the truck is going on randomly and the temp is right where it is supposed to be.

I know I connected it back correctly but I will have to pull the alternator and check it out I guess.
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Old 12-28-2011, 04:12 PM
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I just changed the sensor and I am still getting the code.

My temp gauge will work for a few minutes when you first start the truck and then drops down to nothing.

Regardless I am still getting the p0118 code, any ideas?
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Last edited by sk187; 12-28-2011 at 05:27 PM..
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Old 12-28-2011, 08:16 PM
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Looking at schematic, the sensor grounds itself. It goes through two connectors C127 and C133 and then directly to the gauge. Has to be a badd connection at one of the connectors, at the gauge, or the gauge itself. The sensor that provides input to PCM is not self grounded and connects to A4 and A16. Two sensors, two temp inputs. Gauge is separate from PCM which is where code is coming from.....seems like the problem is illogical.

The gauge and the MIL do not show to be related. One should not cause the other. I'll keep looking.....
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Old 12-28-2011, 08:23 PM
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Does the 99 still have two temp sensors? Thought that changed for 98?
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Old 12-28-2011, 08:24 PM
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It just seems weird they are some what related and both went out at the same time.
The other thing to remember is that the temp gauge works when the truck first comes on so its not a bad connection.


Thanks for helping
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Old 12-28-2011, 08:25 PM
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Quote:
Originally Posted by HeyYou View Post
Does the 99 still have two temp sensors? Thought that changed for 98?
Only one I saw was just to the passenger side of the thermostat, that is what I replaced.
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Old 12-28-2011, 08:27 PM
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Two wire connector?

I think resistance goes down, as temp goes up. Follow the harness for the temp sensor around, see where it goes, and if you have any shorts anywhere.
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Old 12-28-2011, 08:44 PM
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Yes 2 wires to one connector.

I tried to follow it and it jumps right into a group of about 50 wires.


Could the wires be bad at the ect as they tend to get tugged on a little when unhooking it.
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Last edited by sk187; 12-28-2011 at 08:49 PM..
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Old 12-28-2011, 08:52 PM
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Ok, tan wire with black trace is power wire for the sensor. Should be five volts there. Goes to pin 16 on connector 1 at the PCM. ground, or, signal wire back to the pcm is black with light blue trace. That one goes to pin 4 on connector 1.

Disconnect the battery...... unplug C1 from the pcm, and unplug the temp sensor. Now, back probe the wires checking resistance to ground. Both wires should be infinite resistance. Check resistance across the two pins in the sensor connector, should still be infinite resistance. Let us know what ya find.
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Old 12-28-2011, 09:26 PM
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Thanks for the info, this should be fun.

I will let you know.

Thanks again.
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Old 12-29-2011, 12:28 AM
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Haynes shows 2 sensors, but their info is sometimes generic and not necessarily year specific. FSM I have is for 2001. ON a 99 there is only one on the intake, so if there is a second sensor I do not know where it is as I have not had to look for it on mine. Cannot remember if it was 1 wire or two. I'll look tomorrow if you still do not have it resolved. Mine is a 5.2l so I don't know if that would make a difference either.
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Old 12-29-2011, 07:25 AM
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There is only one sensor on a 99.
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Old 12-29-2011, 08:48 AM
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Any idea if the code would cause the temp gauge on the dash to be erratic?
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Old 12-29-2011, 08:58 AM
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What ever is causing the code might, yes. Do what others have suggested.
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Old 12-29-2011, 11:52 AM
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Did you by any chance use (thread/teflon/pipe) tape when you installed the new sensor?
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Old 12-29-2011, 01:21 PM
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Quote:
Originally Posted by DodgeLooney00 View Post
Did you by any chance use (thread/teflon/pipe) tape when you installed the new sensor?
The new sensor had the red paste type already on it from car quest.

The previous one did not have anything on it but they both had the same problem, so I doubt thats it.
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Old 12-29-2011, 01:32 PM
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Were you able to check the wiring as I outlined?

Sensor doesn't need to be grounded to the manifold to work. It's a two-wire... it modifies a signal.

The gauge in the dash is driven by the PCM. PCM tells the central timer module what the gauge should read, and the CTM passes that along to the instrument cluster. The cluster will only display what it is told to. If what it is told is WRONG, then, oddly enough, it will display the wrong information.
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Old 12-29-2011, 01:32 PM
 
 
 
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