Codes not adding up

abrad

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Well, the two MAF sensors are showing IAT values close to each other, but neither is close to the ECT. I would expect IAT and ECT to agree within +/- 5F, at worst. Had the car been sitting in sunshine previous to these readings? Sunshine will start raising the under-hood/intake temperature faster than the engine coolant. The IAT/ECT comparison is best done in the early morning, after everything has stabilized at the same temp for several hours.

If those 102/104F IAT readings are bogus, not accurate for what temp the MAFs are really, then we are back to suspecting wiring or the PCM.

Yes, I know "mA" means milliamps. What I don't have, is any clue about how those values Autel reports relate to AFR/lambda. NB sensors, which I think you have, are always reported as voltage, since they "toggle" from lean to rich at 450mV. WB sensors are reported in AFR or lambda; and usually have the 0-1V NB output synthesized for applications or scanners that can't handle WB data. Milliamps is a bizarre (useless?) way to report O2 sensor readings, so I would be curious what Autel thinks it means. However, I don't think your problem is with the O2 sensing, so probably not worth the bother to find out Autel means.
Car has been sitting inside a stand alone garage, it does get pretty warm in there. I have an outdoor el cheapo thermometer sitting inside, and it was showing about 90°. If I can find my digital thermometer I will check the under hood temp and the coolant temp…

Is there a way to check the pcm, or is that another piece of equipment?
 

billr

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Still, take readings in the early morning, before the garage walls/roof start heating up and radiating heat to the car. The 82F ECT is still not all that close to the 90F on el cheapo. I want to have some reliable basis for checking the IAT.

PCMs are, for the most part, non-testable. You can do a visual inspection of the soldering on the PCB and check the power-supply voltages; but that is about it for a DIYer. What can be done is to check that the MAF sensor is getting the proper power and ground, and that the MAF/IAT signals are getting back to the PCM.

It is probably easy enough to bench-test the IAT function of the MAF assembly, I expect that is simply a (variable) resistance. The MAF function may be tougher, since you would have to flow air through it and the signal may be an analog voltage/current, a frequency, or serial/parallel digital bits. I simply don't have that kind of detailed info on the MAF right now, but will try to dig into it if we can confirm the MAF/IAT readings are not "reasonable" in live-data. Right now, I don't even know the pin-outs of the MAF!
 

abrad

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FINALLY got the briefest of time to do a little more on the temp readings, which are “weird”.

Laser thermometer readings on a few points in the garage gave me temps ranging from 82°-84°, so that’s the baseline for inside the garage, where the car has been sitting the past few weeks.

Thermometer temps on the top of the radiator and the top hose - both readings came back at 82.8°. The IAT reading was 83.2°.
With the old MAF connected, the engine coolant temp was 82°, but the IAT reading was 97°!
Connected the replacement from Cardone, and the coolant temp was - - - 82°! The IAT however started at 86°, then jumped to 91, 93, 95, then settled on 97°!
So, my thinking is that the MAF is ok, and I’ve got a gremlin elsewhere.
The ECM?
The harness? I’ll check the harness at some point, when I’ve got a couple spare hours. In the meantime we are taking it off the road, and the wife will use the other car that her son was using before going to his duty station.
Still haven’t been able to get the time to check the resistance on the O2 sensor, or check compression and fuel pressure, but when I do, I’ll post here…
 

billr

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I will start looking for info on that MAF/IAT assembly. The IAT is usually just a simple thermistor, and that circuit should be easy to trouble-shoot by a DIYer, if we can find the pin-out for the assembly and temp curve for the thermistor. I think it is more likely to be a wiring problem than the PCM, but we also need to find a schematic of the circuit to check the wiring. I can't promise anything, but will search a bit...
 

billr

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Are there two cables connected to the MAF/IAT assembly or just one? (either a 2-pin + a 5-pin, or only a 5-pin). Can you read the pin numbers on the connectors? One variant I find is like this:

2-pin
1) RED/YEL wire IAT signal
2) GRN/YEL IAT ground

5-pin
1) GRN/YEL sensor ground
2) RED/YEL IAT ground (not used if 2-pin connector is present) Very late edit: I think this might actually be the IAT sensor signal, will have to check...
3) RED/GRN MAF +
4) BLK/RED MAF-
5) BLK/YEL sensor power (12V)

Tell me how much I got right, so I can tell if I am going in the right direction...
 
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abrad

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Are there two cables connected to the MAF/IAT assembly or just one? (either a 2-pin + a 5-pin, or only a 5-pin). Can you read the pin numbers on the connectors? One variant I find is like this:

2-pin
1) RED/YEL wire IAT signal
2) GRN/YEL IAT ground

5-pin
1) GRN/YEL sensor ground
2) RED/YEL IAT ground (not used if 2-pin connector is present)
3) RED/GRN MAF +
4) BLK/RED MAF-
5) BLK/YEL sensor power (12V)

Tell me how much I got right, so I can tell if I am going in the right direction...
One harness, 5 wires. Picture attached
 

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billr

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Good, your wire colors correspond to the info I am finding.

Disconnect the harness and read resistance from the harness GRN/YEL wire to ground (engine block or battery negative terminal); should be 0 ohms. Next, with KOEO, read voltage from the RED/YEL wire to ground. Post what it is, but I am guessing 5V. Similarly, read voltage from the BLK/YEL wire to ground, should be ~12V (battery voltage). With harness (still) disconnected, observe IAT in live-data as you go KOEO, see how that temp behaves and if it magically stops again at 97F.

Finally, with harness still off, read resistance between pin 1 and pin 2 of the MAF connector. Post that reading along with the ambient temperature at that time.
 

abrad

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Ok, here’s what I got so far, and I’m not trusting the resistance readings as the battery in my reader was showing as weak, and of course I just happen to be out of that particular battery!

resistance from the green/yellow to ground read 29.7 at the 200 range, and 17.1 at the 200k range

voltage from red/yellow to ground was right at 5
Voltage from black/yellow to ground was 12.2, which was also the reading from positive to negative on the battery
Resistance between pin 1 and pin 2 would not read, which is when I noticed the battery icon flashing on the reader.
so, next trip to the store I’ll have to pick up a 9v battery, then recheck everything!
 

billr

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Why do you say that? My guess, from all the discussion so far, is that there is a problem with the MAF/IAT system; and probably not the MAF/IAT sensor assembly itself. I am trying to help the OP track this down systematically. Do you have a different course of action or procedure to suggest?
 

grcauto

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You have a scan tool that can't be trusted and are using resistance tests to confirm function and that is not good at all. The only test that can be trusted is if the test fails. If it passes it may very well still be bad. Tests that are not conclusive are the very much a rabbit trail.
 

abrad

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Ok, here’s what I got so far, and I’m not trusting the resistance readings as the battery in my reader was showing as weak, and of course I just happen to be out of that particular battery!

resistance from the green/yellow to ground read 29.7 at the 200 range, and 17.1 at the 200k range

voltage from red/yellow to ground was right at 5
Voltage from black/yellow to ground was 12.2, which was also the reading from positive to negative on the battery
Resistance between pin 1 and pin 2 would not read, which is when I noticed the battery icon flashing on the reader.
so, next trip to the store I’ll have to pick up a 9v battery, then recheck everything!
So, just got a chance to look at this car. We took it off the road to save on the insurance, so I’m just going to be tinkering with it on and off going forward.
Double checked the readings, no change. Resistance from harness to ground is reading 29.7 on the 200 ohm setting, and 17.1 on the 200k setting.
still noreading between pins one & two…

only real change today is that the ambient temp was 86°, and the IAT read the same! Engine coolant was reading a few degrees warmer, at 92°
 

grcauto

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I'll say this one more time. Resistance tests are far from conclusive on these low power circuits. You need to load test them.
 

billr

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No reading probing pin 1-2??? There must be something, either 0 ohms or open-circuit; which is it? Where are you reading that ~20 ohms. When you probe 1-2, you are probing the pins of the sensor itself, harness disconnected, correct?

I am disagreeing with above post. Resistance readings on the IAT sensor are quite easy, meaningful, and accurate if it is a simple thermistor; which think it is.
 
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