Experts??????????

Goose · Mar 29, 2018

I've mentioned this before on this forum.

Here's the scene. 2007 Chrysler T&C minivan. A month or so ago, it set a code P0073 for a failed ambient air temperature sensor. The sensor was replaced with a new one from NAPA. Several days later, it set the code again. I couldn't find anything else obvious, so I erased the code. It reset in a day or two. Besides the outside air temp display, the heater and A/C are also affected because they interact with the sensor.

I replaced the NAPA sensor with a Chrysler OEM sensor. Same result. Erase the code and it resets in about a day. I now have the vehicle at a local independent dealer who was a Chrysler dealer before they lost their franchise in the shakeup a few years ago. Their tech has gone through the system with a lot more sophisticated diagnostic equipment than I have and is drawing a blank. He even patched in an entire different heater/A/C control head with no change. He admits he's stumped. All of his diagnostics show there is no problem, yet the problem exists.

Do any of ya'll have any ideas? Thinking back to the days when I worked on avionics systems in jet fighter planes, it was known that of all of the really tough,unheard of problems, probably more were fixed over a beer in the Staff NCO Club than out on the flight line. You'd mention it to a couple of your buddies from a different unit over a beer, and pretty soon someone would think of something that happened once in a different squadron, and the conversation would take off from there.

Thanks in advance for any input.

Grandpa's Fords · Mar 29, 2018

You asked for experts sorry I'm not one. Experienced something similar in a 05 chevy come to find out damaged air damn inside headlight area misdirected airflow just a thought worth mentioning. Replaced headlight mounting and she was back to normal.

Oliver 500 Wa · Mar 29, 2018

Does a check of the live data from the engine computer show that the sensor is reading out of range? If it is, I would look at a problem in the wiring between the sensor and engine computer. If the sensor is an NTC type then an open circuit (broken wire or bad connection) would indicate too high of temperature.

matthies · Mar 29, 2018

Did you or the shop load test the wires from the sensor to the computer or were it ends up? I have a low air buzzer from a truck that I use on problem wires. The fluke will show continuity but the wire can't carry a good 12 volt load on it. With the wires disconnected put 12 volts to one end and hook the buzzer to the other end and then second wire of the buzzer to ground. If the buzzer sings you're good, if not start following the harness. You can leave the buzzer connected and sometimes if the wire makes a better connection it will sound and you know you're getting close. Buzzer part number 268690C91, an IH truck number.

FBH44 · Mar 29, 2018

Grandpa's comment reminds me, we had a new City PD built, and the city court lights would never light up. THey just sat there with some of them very dim. Replaced everything, new bulbs [very expensive ] nothing helped. Come to discover the HVAC engineer had forgot the return air ducts in the court area, and return air had to flow up and around each light fixture. That kept them cooled down, so they never heated up and lit off and glowed. Had the bozo install HVAC return air, and it all worked just fine.

carvel minne farmer · Mar 29, 2018

goose the first thought I had is an intermitant ground issue. on (usually) the right fender well will be a cluster of ground wires and from that will be a small ground wire going up to the big negative cable, sometimes molded into the battery post clamp itself. using an ohm meter wiggle each ground wire and watch the ohm meter. at the cluster of ground wires take out the bolt that holds them down check for corrosion, loose connection on the end of each ground wire. one of those ground wires will also go to the ECM (electronic control modual) that wire would also be a likely suspect.

caterpillar guy · Mar 29, 2018

What about a broken wire or bad ground. Or just put an old fashioned unit in and smile as it works.

JDEM · Mar 29, 2018

Is the outside thermometer still reading correctly? It uses the same sensor.

I know of several people with Grand Caravans that threw the same code. Changing the sensor in front did not fix it. Nor did changing the computer.

I have two Grand Caravans and both became plagued with nuisance computer glitches over time. I just ignore them. Both still run fine and fuel MPGs never dropped.

That said - one of the few errors I have NOT gotten is the one you have - although it is very common in Dodge vans.

Crazy Horse · Mar 29, 2018

We have an '02 Caravan that has had an engine light (sensor I assume) on for over ten years. Now and then I get my son-in-law to reset it with his little hand-held unit. After a week or two, it comes back on. I don't even bother with it anymore, obviously the vehicle is not suffering as much as maybe the environment is suffering. I have no idea what the issue is/was and at this stage of the game, I don't want to find out.

Ken Macfarlane · Mar 29, 2018

Wiring damage, pull your hair out and throw things then return to checking it over again. I would be suspicious of grounds first.

Steve@Advance · Mar 29, 2018

What matthies suggested, load test the sensor circuit, check for corrosion at the junctions and CPU plug, bad grounds.

Not an easy job, trying to work with the tiny wires and ends. The ends can look perfect and not make connection internally.

Jdr315 · Mar 29, 2018

It's a P code so it goes through the powertrain control module. The a/c head probably gets its reading from the PCM. I wouldn't think the a/c control head would have anythi g to do with it. Need to check the wires from the sensor to the PCM. Possibly make and splice in a new overlay harness and see if it takes care of the problem. Sometimes it is the pins in the connectors also. It shares a ground with the cam position sensor so if it is a ground problem it is passed the connection that goes to the cam sensor. If it was me I would check the pins at the sensor and PCM, if those are good and not spread apart I would splice a new wire from the sensor to the PCM.

david from mo · Mar 29, 2018

jdr nailed it. Without checking I think with sensor unplugged 5 volts on one wire.report back if you need more help

WGM · Mar 29, 2018

One of the beauties of refusing to use an authorized dealer. Good luck on your costly endeavor.

dhermesc · Mar 29, 2018

Agreed. If you really want it to cost some serious money go to a dealer pay them a $125 dollars an hour to throw parts at it then shrug their shoulders.

Oliver 500 Wa · Mar 29, 2018

My experience with dealer mechanics is they are not worth a $hit. Last new car I bought went in 3 times on warranty for a non-working fuel gauge. They just tossed in new parts each time and never tested their work. I got tired of them effing around and looked into it myself. Found a connection that was not assembled properly under the back seat. Took all of 20 minutes, a multimeter, and a wiring diagram.

If I couldn't do my own work, I'd find a good independent shop.

Jdr315 · Mar 29, 2018

Come on now, we aren't all that bad. I don't work at a dealer anymore. Spent 6 yrs in one. We did have some guys that were parts replacers and couldn't figure out anything. Bad thing about this field of work now days is not a lot of people wanting to do it. If you do find some one they are fresh out of tech school with no experience.

Jdr315 · Mar 29, 2018

No 5 volt reference on the temp sensor. The PCM just sends the signal to the sensor which is a veritable resistor, resistance changes with temp. When the signal come back the PCM sees the differnent resistance and calculates the temperature.

dhermesc · Mar 29, 2018

My last Ford I bought under warranty was in the shop over 40 times for warranty items. Everything from electrical/computer issues to seats that were frozen in place and wouldn't fold or slide. It would usually take three trips for every item, the first time with an appointment they wouldn't get to it, the second time they would diagnose the problem - but couldn't fix it, and the third time they would fix it. Pretty much covered my experience with Ford at three different dealerships in three different towns. Never found one that I would even think of recommending. So I bought a Kia, I have very little idea how good their warranty work is. In over 100K warranty miles the two vans had only been to shop once for a warranty item - some rubber bushings in the steering on the first one we owned.

Ted in NE-OH · Mar 29, 2018

Take it to a bonafide Chrysler dealer they have factory backup when they hit a tough one. I'll bet it would have been cheeper.

johnlobb · Mar 29, 2018

chryslerminivan.net has really helped me a lot. The generation 4 encompasses years from 2001-2007, so you need to ask your question on the gen 4 forum. Good luck...

pete 23 · Mar 29, 2018

With the common description of an expert being someone away from home, well, I am home so cannot qualify as EXPERT. Not a auto mechanic either by trade either. Red tractors was my game for , well, 60 years. From the sound of most guys on here, glad I am not required to work on their cars.

I was just wondering though. Before it sets a code again , after replacement of the sender, does heater and air cond work properly until it pops a code (or light) again.

Oliver 500 Wa · Mar 29, 2018

The primary purpose of the air temp sensor is for the engine computer to help calculate the air density coming into the engine to determine the proper amount of fuel to inject. The operation of HVAC is a very secondary use of the sensor's input

steve_in_mo · Mar 29, 2018

A bad body control module can send an error code
for a sensor. If it's intermittent it's hard to find.
Learned that the hard, expensive way.

steve_in_mo · Mar 29, 2018

I'm not an expert but I have experience in this.

MARK ROBKE · Mar 29, 2018

I agree with jdr315 in his post where he has the wiring diagram. I am a retired truck tech,and have had to make up an overlay harness a few times to correct an intermittent fault.When you go thru all the diagnostic checks in the fault tree, replaced the sensor twice,and the problem still reoccurs,then it is either the PCM,or the wiring.Wires are easier,and CHEAPER,to try,before a test PCM ! The wiring may ohm out good,but still be at fault. If the harness has any plug connections,a terminal may pull out when you unplug it, but push back,making poor contact,when you plug it back together because the plug body is bad,not locking the terminal in place.
So what I would do after all this, is make and run an over lay harness for that circuit. Good luck,Mark.

jimg.allentown · Mar 29, 2018

How about...
I would check over the harness carefully. Over the years, I had several strange problems present to me. Things like cutting out when put in reverse to acting up only while climbing a certain hill. The culprit every time was the harness. In some cases rubbed through on a metal part - NOT obvious until examined closely. One turned out to be a corroded connection at the ECM.

Something to keep in mind is that electronics are sensitive. Automobiles are a very harsh environment. The fact that they work as well and for as long as they do in nothing short of a miracle. By necessity, wiring has to be located close to metal parts. Some of those metal parts are known to move around frequently. When they contact the wiring, there is usually no problem. After time, though, things get rubbed too many times and make contact with a conductor.

So, my advice is to examine the connectors, look for potential contact, check grounds, and recheck everything until you find the problem. I strongly suspect the engine control module connector. Disconnect, check for corrosion, and reconnect.

4play · Mar 30, 2018

I question the ability of the shop you took it too, since he seems to be focused on the HVAC system. It's been mentioned but this sensor is wired to the engine computer (PCM) hence the "P0073" (P codes = powertrain faults). If you could monitor the sensor temp and voltage value from the PCM data it would help. This sensor works off of a 5 volt reference provided by the PCM. The sensor should have 5-volts on the violet/green wire with key on. Unplugged the PCM should also indicate 5 volts on the sensor voltage data value and temp reading of -40*. If you shorted the two wires together with a jumper the sensor data readings should be near 0 volts and read 130*

I doubt you have a problem on the sensor ground circuit to the PCM since it is shared with most of the other powertrain sensors. The sensor ground circuit splices to all the other engine sensors near the a/c compressor clutch take-out in the loom. My guess is a loose pin or possible broken 5V ref wire to the sensor. Monitor sensor data and wiggle/tug on wires/harness while watching for a change. Look for rub spots, pinch zones or areas where wiring looks like it might be moving around. Crash repair spots can be popular for wiring problems, rodent chew spots too.

BobReeves · Mar 30, 2018

Agree with 4play, very possible the 5 volt supply is the problem, either wiring or an issue with the computer.

Helped a buddy fix a Caravan several years ago, think it was an 02. CPS wasn't working and a little trouble shooting told me we were not getting the 5 volts out of the computer. Not wanting to put any more money in it I disconnected the 5 volt wire from the computer and built up a little 5 volt regulator circuit using a 7805. Last I heard that van was still running with that 5 volt regulator three years after our fix.

I like Caravans, have owned 5 and presently have an 05 that the wife drives and I drive a 2013. One before the 05 was a 94 that I sold running with 260,000 on the clock.

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