jl4c

I know what each code stands for, one is low voltage from the MAP sensor and the other is low voltage from the IAT sensor. From searching the archives here and at other diesel sites I can see that several people have reported getting these codes at the same time and the only fix that worked was a new ECM. It seems to be most common in the 2002 ETH/DEE (HO, 6 speed) trucks, which is what I have.

The truck idles perfectly but won't build higher than about 4psi of boost--it defuels and runs rough if you press the accelerator pedal down to build boost.

Interestingly, if I load my Smarty software into the truck, it runs fine. There are just those pesky codes turning on my check engine light. Apparently the smarty software ignores inputs from the MAP and IAT sensors.

I've tested the IAT sensor and tried a new map sensor to no avail. Before I plunk down for a new engine ECM, does anyone have any other ideas?

diesel_burner

I had the same thing happen to me last winter. The Cummins Tech said he couldn't tell me why it failed. But I will tell you one thing, 2 months after replacing my VP-44 I had to replace the ECM. Things got $pendy there for a while.

robert78.5

I am having some issues also. Did you read the volts on the harness side of IAT sensor plug? With key on the first position, my manual says there should be 12 volts from the wire with the blue stripe. I am showing 0.03 volts. Did you happen to test yours. I would be curiuos to see what another truck reads.

diesel_burner

I didn't read mine just limped it down to the dealer and said fix it. I would have took more time but I was moving from North Dakota to New Mexico in 2 weeks and had to get it done.

jl4c

Are you talking with the sensor attached and "pin pricking" the wire? Or do you mean with the harness disconnected from the sensor and measuring relative to the engine ground? (Sorry, I'm a mechanical engineer--electronics is a weak spot for me...)

I've checked the MAP sensor harness (while disconnected from sensor) and measure 4.98V feeding the sensor. (4.8v - 5.3v is what is supposed to be normal with key on, engine off.)

robert78.5

Yes i unplugged the harness and took a reading from the wire end of harness. On MAP harness the input was 5 volts, but on my input for IAT harness (wire with blue stripe) according to my Haynes manual should be 5 volts but i am getting 0.03 volts, I do however get 5 volts on wire with red stripe going to IAT sensor. Maybe the manual is wrong. Does anyone know which wire is the feed wire to IAT sensor?

jl4c

On my 2002 the following wires/colors apply:
MAP sensor (potentiometer)
orange is 5V supply
BK/LB (black w/ light blue stripe) is sensor ground
GY/RD (gray w/ red) is the sensor signal

IAT sensor (thermistor)
BK/LB is (again) sensor ground
BK/RD is the sensor signal
There is no 5V supply to this sensor (??how does it work then??)

Both sensors have a common sensor ground (the BK/LB wire)

robert78.5

Thats what i figured, the book shows that the blue stripe wire is feed, when infact it is the red strip wire. It has 5 volts so it looks like i am set to go.

Number47

IAT works by changing resistance and varying the voltage return to the ECM, so you should have, most likely 5 volts in, it may also be 12volts but not likely. thus the name(not trying to sound like a dick, trying to educate and help) thermistor, THERMo resISTOR. the map sensor work the same as tps but smaller, boost pressure acts on a thin metal disc and move the pin on the coil.

jl4c

No offense taken. My question was more along the lines of why does the map sensor have THREE wires going into it and the IAT sensor has but TWO?

robert78.5

So does anyone know which color going into IAT sensor is the feed wire? Red stripe or Blue stripe?

jl4c

Please re-read my post above. The information I gave above is right out of the Dodge service manual.

BK/LB is sensor ground
BK/RD is the sensor signal

jl4c

Since the MAP sensor runs from a 5V supply voltage from the ECM, I hooked up three brand new AA batteries in series (not quite 5V but close enough). Then I removed my map sensor from the engine and hooked up the battery pack to the 5V supply and sensor ground terminals on the sensor. Then I used a voltage meter to measure the voltage between the output signal and sensor ground.

Doing so I measured about 0.9V. Then I used my air compressor with the air hose rubber-tip adapter and regulated the pressure down to 20psi to pressurize the map sensor and re-read the voltage--1.34v or so. I did the same test to a brand new map sensor and got the same values (within 0.01v).

I reinstalled the map sensor in the engine and used some straightened paper clips to back probe pin 11 (sensor ground) and pin 8 (sensor signal) and pin 10 (5V supply) at the ECM itself. I got the same voltages so I believe that my wiring harness is OK.

The last thing I'm going to try is to purchase some high ohm resistors from Radio Shack and connect them in series so I can "tap off" any voltage that I want and feed that directly to the ECM via the map sensor connector.

If that final test doesn't convince my ECM that I have boost then I think it's time for a new ECM.

The funny thing is that if I load my smarty, the truck runs fine. If I flash back to the stock setting the truck runs in limp mode.

I bet if I was to open up the ECM and look at the PC board inside, I'd find a bad connection to pin 8.

Any additional thoughts that anyone has on the subject would be appreciated.

jl4c

Picked up some 22k resistors and fed the ECM a signal of about 1.3V. Still no joy. Ordered a reman ECM yesterday--should have by tomorrow. Will advise if this fixes it.

jl4c

Unfortunately the answer to this question is an unqualified yes. I learned a whole lot more than I cared to, but got it all fixed for WAY LESS than the dealer or even Cummins wanted. All totaled up I spent about $700 including two trips to the diagnostic hookup. I bought my reman ecm from Autocomputerexchange on eBay--$524 including return shipping--and comes with a lifetime warranty.

Because the PCM reported both map and IAT sensor failed at the same time I was pretty sure the ECM was the problem, especially when I could test them both and knew they were good and knew they were sending signal to the ECM.

Hope this helps someone else. Free free to email me at turbodsl <at> jl4c <dot> org if you need more info about this repair. (Make the appropriate substitutions in my email address.)