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lamothe1 03-05-2007 11:14 AM

'2001 Malibu temperature sending unit not working
My 2001 Malibu temperature gauge stopped working (stays on cold) so I disconnected the sending unit and grounded the 2 pins to see if the dash gauge would go up to hot - Nothing happened.
In the past I’ve had trouble with the ignition switch contacts becoming burnt and causing some of the dash gauges not to function so I cleaned them with fine sandpaper, so again (hoping this was the problem) I disassembled the switch and cleaned the contacts, reassembled everything started the car and the check engine light came on. I went to auto Zone and used their Diagnostic machine and it gave me a code P0118 (engine coolant temp. circuit high input) and code P0128 (coolant temp. below thermostat regulations). I then erased the codes and the check engine is now off and the gauge still doesn’t work. Also when I shift the trans to Drive it hits REALLY hard like the engine was turning about 2500 RPM’s other wise it shifts fine thru the gears while driving the car. It shifts from Neutral to Reverse fine it’s just from Neutral to Drive that it bangs.
Did I blow some portion of the PCM or is it the temp sensor is bad and the PCM is getting some weird reading and causing the tranny to bang into gear?

docvette 03-05-2007 03:37 PM

Doc here, :pimp:

Is this a Digital dash?

If mechanical, and you did not get a response from grounding the sender wire, it would indicate the wire or gauge is at fault..

Check the sender wire back to the instrument bucket with a DVOM, set to OHMS, R X 1, Calibrated 000, It should read "000" from the sender to the bucket, If infinite, it's open and needs repair or replacement.

Next if good, locate the "S" terminal on the gauge, (at the laminate card) jump it to ground, and watch the gauge, If it pegs, the gauge is good, and you may have a bad connection at the laminate card or an open trace.

If it does not move, check the "I" terminal for 12 volts at the gauge laminate card) If missing, check the connection and/or fuse.

If it is good, check the "G" terminal on OHMS (no ignition power on) R X 1, Calibrated to "000", it should read 000, if not, you have a bad ground at the card.

If all are good, your gauge is at fault.

The RPM's may or may not be related, (computer thinking it's at high idle, cold, and telling the transmission to hang in at a higher idle..) so were it I, I'd fix the gauge may not have a secondary problem.

Doc :pimp:

lamothe1 03-06-2007 01:20 PM

I drove the car today and the check engine came back on. Is it possible that the sending unit is bad which gives the PCM an out of range reading. The gauges are mechanical and the RPM at idle is about 500 or so. Also, there are two wires to the sending unit I think one was yellow and the other was black or some dark color, is one ground and the other to the computer or do they both go to the computer? I think the service manual said something about 5 volts to the sending unit and something I didn't understand about so many pulses. Is a DVOM a digital volt meter and does "back to the instrument bucket" mean to the back of the dash and is the laminate card the printed circuit?

vicrod 03-06-2007 03:16 PM

Any car newer than 10 years old I assume; computer controls it unless found otherwise.
Check out and subscribe to that particular car.
That will give you all you need.
Unfortunately, shorting out a computer controlled device is not something you find recommended on late model cars.
Get out the checkbook.


docvette 03-06-2007 03:26 PM

Doc here, :pimp:

OK, If the Gauge or Wire or sender were "open" the computer would probably see an open loop situation..Setting off the Check engine light..So you need to troubleshoot and eliminate Those first..

The sender should have a resistance to ground when measured, (you'll have to look it up for your car or ask a parts guy..) remove the sender, get a pan of boiling water (212 degrees) and a accurate lab (or meat) thermometer, next, hook the sender up to It's plug, and tightly wrap a bare ended ground wire around the sender body, and ground it to the engine..

Immerse The sender in the water CAREFULLY, and monitor the gauge in the car..It should report..If not remove the sender, clip your DVOM, set to R X 1 , OHMS scale, calibrated to "000" . to ground and either pin on the sender, immerse it back in the water, (be sure it's still 212 degrees) and watch your meter..It should read at or above the resistance Specs for the sender..Watch as the water cools, it should decline or increase in resistance readings (depending on how the sender is orientated) .. Do the same for the other pin..If it HAS a reading, It's probably good, If it's infinite, (no reading changes) It's bad..Replace it.

If the sender checks good, find the wire that goes AWAY from it to the gauge bucket and/or computer, (follow the color code to the pins ) You SHOULD get a manual for your car (auto $21.00) for the pin numbers assigned..Using your DVOM, set to OHMS, R X 1 , Calibrated to "000", measure the wire to BOTH should read "000" , in no reading OR the reading fluctuates , repair or replace the wire..It's broken, burned or has a bad pin..CLEAN and burnish the computer plug pins AND backplane with a Good electrical cleaner, and burnishing tool..BE careful in this area and disconnect the battery cable.

Next Check the wire between the gauge and / or the computer or sender the same way, from the laminate card, and the sender or computer..It should read "000" if not its bad, repair or replace as required..

If that is good, remove the laminate card from the bucket (it should all come as a unit, gauges and all..Inspect it for burned traces..or bad pins in the plug well..measure between the "S" , "I", and "G" pins as before, for a "000" reading..If any are infinite, the pin, or trace is bad or burned open..a new laminate card is in order..

If all is good, the gauge is bad..replace it as needed.

Yes, a DVOM is a digital Volt ohm meter..

A "Bucket" is the metal well the gauge sub~cluster sits inside of..remove that and you should have access to the laminate card and gauges..

A Laminate card is a (in GM cases, anyway) thin "filmy" flexible card with printed circuit traces on TOP and BOTTOM,(and sometimes in the middle) of the laminate to direct the signal flow to the proper devices..(gauges, lights, ect..)BE CAREFUL with it, It is fragile!! If you bend it too far, it may snap a trace..It should BOLT right onto the gauges.

The Black wire is NOT a ground, but rather a low signal From the Computer to the sender (DO not ground it, it can damage the Quad buffer / Driver on the computer) It works by sending a "Clock pulse" or a series of low pulses to the sender as opposed to a hard ground, that operate sender, in "sync with the computer damands..The other side should be hard data..(or even a fused 5 volts)..

Hope it helps out..

Doc :pimp:

lamothe1 03-07-2007 01:10 PM

It looks like I'm in for a busy weekend. I'm worried about the Black wire that I should NOT have grounded, I hope that it didn't blow the computer. thanks for all the info. I'll post the results :sweat:

docvette 03-07-2007 02:03 PM


Originally Posted by lamothe1
It looks like I'm in for a busy weekend. I'm worried about the Black wire that I should NOT have grounded, I hope that it didn't blow the computer. thanks for all the info. I'll post the results :sweat:

Doc here, :pimp:

Keep us posted!

The quad driver/buffer may have been able to absorb the "hit" provided you didn't run it too long..Their pretty stout..

On those, the usual config is one is reference pulse, the other is sender..AND one more thing, are you sure you got the right sender? GM also uses traditionally on the left head ( 1 pin, Gauge) and one on the right head (2 pin Computer)..check to be sure you have the correct one.

Doc :pimp:

lamothe1 03-08-2007 01:27 PM

The one I unplugged was right below the Thermostat housing, it has two pins and is on the side of the motor that's toward the front of the car. Is that the one that activates the dash gauge and is there another on the firewall side?

docvette 03-08-2007 03:49 PM


Originally Posted by lamothe1
The one I unplugged was right below the Thermostat housing, it has two pins and is on the side of the motor that's toward the front of the car. Is that the one that activates the dash gauge and is there another on the firewall side?

Doc here, :pimp:

The two pin on the housing is probably the computer..

There should be another on one of the heads, below the manifolds, that is a one pin ... that would probably be the gauge.

The one on the (Firewall?? ) side, is probably Oil sender.

That is if it is configured like a Pre 2000 SBC.

Doc :pimp:

lamothe1 03-08-2007 04:19 PM

One more question.
If there is another sending unit on one of the heads that seams to be tapped into a water jacket and has a single pin, would it be safe to ground it out to see if the temperature needle moves?

docvette 03-08-2007 04:24 PM

Doc here, :pimp:

just have someone watch the gauge, and , with key on, without the engine running, quickly ground it, If the gauge "Jumps" that is the one you want.

Doc :pimp:

lamothe1 03-08-2007 04:41 PM

Thanks, I'll work on it this weekend :cool:

lamothe1 03-12-2007 12:52 PM

Well it’s fixed. I checked the wires from the sending unit and they were O K, next I removed and disassembled the gauge assembly but there weren’t any of the letters “S” “I”, etc on the printed circuit board so I put everything back together, noticed that the temp. gauge was working so I reset the PCM and now everything fine. It must have been a one of the pins on a plug wasn’t making a good contact. Thanks for all the input.

docvette 03-12-2007 04:01 PM

Doc here, :pimp:

KWEL, you may have had a bad cluster ground, common problem that "rights" itself after working on the cluster..Glad to hear it works! :thumbup:

The "S" terminal is for sender..

The "I" terminal is for 12 volts..

The "G" terminal is for ground..

Should you ever need it again, not all are marked or marked on the rear of the gauge not the laminate.

Doc :pimp:

lamothe1 03-13-2007 04:32 PM

On the back of the gauge their are 4 pins that plug into the circuit board one isn't used and the other 3 are marked #1, #2 & #4 and in the center between the numbered pins is "M2"

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