Originally Posted by Dennis Wilson

Hi Bill Curlee. I posted a few months ago. about my elec. issues. I have replaced the coolant temp sensor, cleaned the door connectors multiple times, cleaned the chassis ground plugs by the front of engine, `03 Z06 70,000 miles. car will be fine for a few hundred miles, now the latest is the car will misfire, and the DIC will say "low oil temp" all other gauges normal, Then it might run fine with the oil temp reading low, Then after stopping and restarting the temp will be normal again, and will run fine , Got home and there were NO codes. either C or H. and everything was normal again. What do you think? Thanks, Dennis.

Originally Posted by 8VETTE7

First, dielectric grease in NON conductive ie an insulator when applied to contact surfaces:

http://www.tech-faq.com/dielectric-grease.html

NOT a good idea to apply to contact surfaces if that is what you did.

P0118 is reporting high resistance from the Engine Coolant Temp Sensor. High resistance is viewed as COLD by the PCM.

P1114 is reporting Low Voltage seen by the PCM. Low resistance equates to low voltage being seen by the PCM or an engine temp of 282F or more..


P1115 is reporting High voltage seen by the PCM. High resistance equates to high voltage seen by the PCM or an engine temp of minus 36F or more.

Since you replaced the temp sensor the sensor itself is unlikely to be the cause of these codes. The wiring between the temp sensor and the PCM is likely the cause.

I would pull the battery and the shelf it sits on and check for acid damage from a previously leaking battery. Wires to the PCM are directly below the battery.

Connector C2 has the brown wire from the engine temp sensor in position 60 which is the low reference. Connector C1 has the yellow signal wire for the coolant sensor in position 74. Likely the wire(s) are damaged between the PCM and the engine temp sensor causing the PCM to see widely varying resistance values..


You may also have a bad connector to the temp sensor.

Since the engine temp is a critical engine control input to the PCM the fact that is is seeing alternately very high and very low engine temps would cause the engine to run very erratically.

Originally Posted by 8VETTE7

When you read the codes did any of the sensors report NO COMM???

For example A0 LDCM NO COMM or A6 SCM NO COMM etc.....

Originally Posted by 8VETTE7

If the U1160 was listed under the 10 PCM then the PCM had lost communication with the LDCM..

That is not the same as an entire sensor module that has NO COMM next to its name.

When you list codes you need to take note of which sensor a Uxxxx codes is listed under. For example U1160 means loss of communication to the LDCM and there are several sensors that need to communicate with the LDCM so knowing which sensor lost communication can be important.

Perhaps you could pull the codes again and carefully look at each sensor to see if any one of them has NO COMM next to its name. I assume that you are pulling codes and not just expecting them to show up in the DIC automatically???

What I'm looking for is a situation where a single sensor causes major problems on the serial data buss that affects many other sensors since ALL sensors share the same serial data buss.

Originally Posted by Dennis Wilson

As of now , I have cleared all the codes. Is there a way to retain them after they cleared? I think the lost comm. w/xxx was when the codes were "10 PCM 1115 H C and PO 118 HC " and U 1160H. Thanks for your help. The car will run ok for a few mi. before the problems start again.

Originally Posted by 8VETTE7

If that is what was displayed in the DIC then that is exactly what I determined from the codes you posted above. When that is happening the PCM cannot use the coolant temp to properly determine how to control fuel and timing to the engine and as a result the engine will run erratically.

You need to chase down the electrical problem with the temp sensor. I suggested damaged wires and/or bad connector to the temp sensor. That should be a good start point.

A complete list of codes taken the next time the engine is running erratically BEFORE you shut off the engine will provide added input for diagnosis.

To pull codes with the engine running you must use the RESET button to clear any messages displayed in the DIC and then pull codes as normal.

Originally Posted by 8VETTE7

Usually when the black plugs in the drivers or passenger doors are problematic there are other tell-tail signs that are present. Often many different sensors will have codes (usually lots of Uxxxx codes which are loss of communications codes) or one or more sensors will report NO COMM next to the sensor name, or lots of messages will display in the DIC such as reduced power, ABS, TC etc. That is why I am interested in ALL the codes your car has stored after the symptoms occur.

The interesting thing about the two symptoms you are having (fluctuating coolant temp and low oil temp) is that the wires from both those sensors go back to the PCM which interprets the electrical signals and then sends messages over the serial data buss to the IPC to be displayed. Since leaking battery acid is a fairly common event on the side post C5's I would personally start with the removal of the battery and the tray the battery sits on and look for wiring damage from acid spills. One other possibility is the cumulative effects of excess heat from long tube headers over many years. Perhaps some wires have been cooked by that heat. Either way the area I would start with is around and under the battery since that is where the PCM is located.

If you can get the car up in the air I would also look at the battery positive connection point at the starter solenoid. Again the cumulative long term effect of excess heat from LT's is to fry wires and sometimes have the positive battery connection at the starter solenoid become loose.......

Originally Posted by 8VETTE7

When you read battery voltage using the dash gauges with the engine OFF and key ON the values that you see are all but worthless. The represent the "LOADED" battery voltage since many C5 electrical circuits are providing load when the key is in the ON position. Further, the ignition switch is between the battery and the gauges so any pitting/carbon buildup will further lower the numbers being read.

With the engine running you read approximately the output voltage of the alternator. Approximate because the starter solenoid connection is between the battery and the alternator and again the ignition switch is between the battery and the gauges. Loose or corroded solenoid connection and/or pitting/carbon buildup on the ignition switch will reduce the value being read on dash gauges.

To accurately know the battery voltage you need to use a digital multi meter across the battery posts, no key in the ignition and prefferably with the neg battery cable disconnected. That is because the hood light might otherwise be ON adding load and the BCM may NOT be in sleep mode and hence adding load.

Don't make any decision on battery replacement until you measure the battery voltage with a digital multi meter and also have the battery load tested. Most auto parts stores load test batteries free. Make 100% certain the battery is fully charged before it is load tested to get a correct evaluation of the battery. A good battery at full charge will measure 12.7 to 12.9 volts or more with no load on the battery.

Originally Posted by Dennis Wilson

I am still going to check the items listed above, But I`m starting to think I got a bad battery 6 months ago. Just went and checked the volts in DIC and analog. this morning and it was 11.3 11.4 I never remember it reading that low before, even after sitting for weeks. Will be taking back to Autozone for check and poss. replace. I remember similar problems, When it was time to replace batteries in the past. But it was always after 4-5 year s. Keeping fingers X`d that batt might be the prob.