I am having an issue with a v6 Camaro of a friend of mine, the PCM & Dash gauge temps are about 30-40 or so degrees off.(see pictures below)
How can this be the case or what would cause this?
I have changed out the Coolant temp sensor 2 or 3 times , so I just thought it was the Dash cluster , I replaced that with another one & same issue.

I have driven the car around and the dash gauge will go all the way to 260 but the PCM never goes about 195 or so ( has 190 thermostat)

so can someone please help me figure this out.

its being a PITA!!

Thanks in advance

 

Most likely it is resistance in a connector or a wire, Or a wire too close to exhaust getting hot and building resistance. Depending on the year it could be an issue with the body control modual.

 

Thanks for the response.
Now sure how i'd go about testing the resistance ?'
Can you elaborate on the BCM issue I am working on a 1997 and I've suspected the BCM on a slight battery drain (new battery but drains after sitting 2-3 weeks ) also I walked outside one day and the door locks were locking & unlocking for no reason ( probably causing the battery drain) ,so I think that issue may be the BCM for that issue ; Just didn't' think about it causing an issue with the cooling as well.

 

Sorry I do not memorize what system any one car uses but there are two ways they can work.

“One wire to the sensor.” BCM outputs power into the sensor. The sensor allows the power to flow to ground. As the sensor gets hotter less power is allowed to flow. The BCM measures the flow and sends a signal to the gage. (Mili amp system)

“Two Wire” Power is sent to the sensor and returns to the BCM. In this case instead of power flow, voltage is read. As the sensor gets hotter the resistance rises and less voltage get to the source showing a hotter temp. (Voltage system)

The two system are very different from an engineering point but for the mechanic they are similar. The major difference is in a two wire system you need to verify that the 5 volt signal is getting to the sensor and that the resistance back to the source is in spec. There are many things that can affect the reference signal.

Resistance in a wire or connector is measured in ohms on a multi meter. I have tried to walk people through electronic diagnoses before with almost zero luck. The trouble tree in the GM manual is the best way to do it. Some PDFs of manuals can be downloaded from the manual forms on the front page at the bottom of these forums.

GL

 

may just need to unplug the pcm and check for bad or dirty connectors. gorn, so a bad wire with only one wire within the many in the sensor wire connecting to the sensor could show a higher temp?

 

With a one wire system the controller tracks the amps it takes to power a circuit to maintain a voltage level. The sensor is the resistor that is is suppose to change as it get hotter. So the hotter the engine sensor gets hotter it builds resistance and requires more amp to maintain voltage. Any wire damage or bad connector will increase resistance, I have not heard of a problem that would cause a wire or connector to have less resistance than new. A bad connectors resistance would be added to the resistance of the sensor causing a high reading.

The 2 wire system is the same way you just need to verify that the 5 volts is getting to the sensor..

Low temps are normally air in the coolant, dirt covering the sensor the sensor or gage.

 

looks like the 97 had a three wire sensor, at least in the parts picture the sensor has three prongs and wire plugin also has three wires.

 

I do not remember working on a three wire version. I wonder if they just supply a ground to a two wire sensor. That way they do not have to worrier to much about the block ground or the sealer on the threads building resistance.

 

Sorry everyone for not getting back to you before now , I wasn't getting notified of the messages... not sure what is up with all that.
OK so to give a little ore insight on whats I've done & whats going on..

1. @craby , you are correct this is a 3 wire system ..( see diagram below)
2. @Gorn , It does appear that the 3rd wire is just a ground , it ties in with other grounds about mid ways of the engine
3. I have replaced the cluster (yes AGAIN) this time with a good Known one..still getting pretty much the same reading

Starting taking the wires out of the wire loom & can Not get to the back of the engine to get the wires out


Also to let you know what's been done to the car ,
The Upper & Lower Intake was replaced ( but I think it was having the same issue before that , but not positive) because of an external leak. but I know it's had this issue since the intake as replaced

Are they anyway that replacing the Intake could had caused this ( my opinion is NO , but.... ) ?

I have checked to make sure they are no water in the oil or anything ... sorry right now I am aggravated and "grasping at straws" as to what the issue could be

One question is , which wire should I focus on , the wire going to the Gauge (Which is reading wrong ) or one of the other wires ?

but from the drawing below it appears that the gauge wires leaves the sensor and goes straight to the gauge ?

again thanks for all the help & the help i know ya'll will give

 

one wire is ground to the pcm one is temp to pcm, one is temp to gauge. check ohms at both temp gauge and temp pcm wires to see if they come out the same. the gauge ground must be common to cluster.