IAT Always Reads 32°

[CruelJung]

Earlier this year, I solved a cold start issue with my 2008 Yukon XL (5.3 LMG) by replacing my ECT sensor. I discovered a few other issues along the way to that fix and one of those issues is that my intake air temperature consistently reads 32°, regardless of environmental conditions or engine temperature. Installing a new MAF sensor did not fix this reading, so I’m presuming this is a problem in the connection between the MAF and ECU/PCM. No CEL, trouble codes, or obvious (to me) operational issues, but I imagine my engine would benefit from an accurate IAT read. The last thing I tried was a cheap cable tracer from Harbor Freight and that did not pan out for me.

Does anyone have any advice or experience with diagnosing/solving this problem?

 

[j91z28d1]

looks like it's pin D tan/black and E tan. at the maf and pin 38 tan and 37 tan/blk at the ecm.

if you can get to it might ohm put the wires at both ends.


with the sensor unplugged it should read across D and E

32deg 5119- 5892 ohm
68deg 2290-2551 ohm
104deg 1096-1238ohm
176deg 312-370ohm

might at least let you know if the part is OK before you start searching thru the harness

 

[CruelJung]

looks like it's pin D tan/black and E tan. at the maf and pin 38 tan and 37 tan/blk at the ecm.

if you can get to it might ohm put the wires at both ends.


with the sensor unplugged it should read across D and E

32deg 5119- 5892 ohm
68deg 2290-2551 ohm
104deg 1096-1238ohm
176deg 312-370ohm

might at least let you know if the part is OK before you start searching thru the harness

I’ve been procrastinating, as my electrical experience is severely lacking. I managed to learn how to de-pin my MAF connector (not necessary, I know), locate the tan + tan/black wires and the pin locations on the J1 ECM connector. With my cheap Cen-Tech multimeter, I’m getting about 5.6 ohms from the D/E to 37/38 with the setting at 200 ohms. This was done with the negative battery cable off, the tested wires disconnected from both the MAF and ECM, and the multimeter probes applied at both unplugged ends.

What do I do with this information? Did I make any mistakes? Please advise, thank you!

 

[CruelJung]

Semi-Solved: I decided to cross-reference my DiabloSport scanner with another tool and it seems my IAT sensor is in working order.

Next step will be getting DiabloSport/Holley to explain why my Predator2 scanner is telling me that my IAT is reading 32 degrees all the time.

On that end, it’s worth noting that my ECM is programmed to the Diablo (93 octane) tune and that I have previously changed the tune back to stock (w/ AFM disable) to check if that corrected the IAT read (in the case of it being a data point manipulation, as part of the Diablo tune), and the IAT live data displayed the same 32 degrees.

So, I will keep updating as the story unfolds.

 

[Fless]

Are there any other IAT PIDs that can be selected on the DiabloSport? Or just the one?

 

[CruelJung]

Are there any other IAT PIDs that can be selected on the DiabloSport? Or just the one?

I am glad you asked that. After re-visiting the PID menu, it seems “Power-Up IAT” displays the expected data for my intake air temperature. I suppose I should re-name this thread to “Paranoid Delusions of a Dangerously Tenacious Novice.”

I was not able to get Diablo/Holley on the phone and I would like to know if my scanner/tuner is in need of a calibration or update of some kind. The PU IAT (to me, at least) is a bit counter-intuitive vs Intake Air Temp. Perhaps it’s a feature, not a bug, though.

 

[j91z28d1]

that's a odd one.. I have seen key on iat saved and used as part of the startup routine to avoid heat soak rich cranking. but nothing you'd need to know or see as a monitor.

weird mostly useless pid to be able to display. most consumer grade stuff avoids options like.

its ridiculous getting anyone useful on a phone or even tech line anymore. you might have more luck with a email sent to their tech department if you can't find it. that way when the tech line guy has no idea, he might take the 2 secs to forward it to an engineer. if he's interested, you might get a reply but probably not either.

glad you found it wasn't a wiring issue after all.

 

[CruelJung]

that's a odd one.. I have seen key on iat saved and used as part of the startup routine to avoid heat soak rich cranking. but nothing you'd need to know or see as a monitor.

weird mostly useless pid to be able to display. most consumer grade stuff avoids options like.

its ridiculous getting anyone useful on a phone or even tech line anymore. you might have more luck with a email sent to their tech department if you can't find it. that way when the tech line guy has no idea, he might take the 2 secs to forward it to an engineer. if he's interested, you might get a reply but probably not either.

glad you found it wasn't a wiring issue after all.

There are some PIDs I can look at that are very clearly "commanded" values (it's even in their titles). I suppose it would make sense that 32-degrees is an intentionally false, commanded value for cold cranking purposes--tune or stock--and I have noticed that my fuel trims do start rich with close to a 1k rpm idle that calms down to where I tuned it (650rpm) within 30-60 seconds.

Without having spoken to anyone from the manufacturer as of yet, it seems to me that the data values and PID names are mismatched; 32-degrees would make more sense as the "Power-Up IAT" value, and the live (accurate) temperature reading as the "Intake Air Temperature" PID. Whether this is a glitch unique to my product or a general "feature" is something I would like to know, when I finally catch someone on the phone. We shall see. In the meanwhile, yes, I am glad my IAT wiring is good and that my tuner/scanner is at least reading accurate information (regardless of its strange categorization in this case).

One of the next hopeful items on my agenda: re-looming, re-routing (where appropriate), and re-attaching the engine bay wiring to where it belongs or would be better off. So, perhaps I didn't *entirely* waste my time learning a few things in that area.

 

[LoggNM]

Hey CruelJung (et al.) -

I have an open circuit somewhere between my ECM and IAT sensor on my 2011 Yukon Denali XL L04, so the ECM recognizes the voltage is above range and substitutes a plug value. Truck runs but has a permanent P0113 code that I need to resolve. I know the tan and tan/blk wires at the MAF/IAT connector are the ones to trace, and I don't have +5V at the IAT so I believe the problem is on the power side of the sensor. I can visually trace the route back and up over the motor to the ECM, but I don't see a definitive pinout or diagram that let's me trace the wires to the ECM connector. Do you or anyone have a suggestion on which page of the 2011 GM upfitter pinout doc is appropriate for an L94 (6.2 with VVT and AFM)? I believe the circuit number is 472, and I can find multiple pinouts that relate to the IAT Sensor Signal but none specifically identify where they conenct at the ECM connector. I'd like to avoid trying to trace all the tan wires in the harness, wchih might work but might also create more confusion. If I can confirm the ECM end of the circuit, I can trace backward from there.

I bet this is a simple wire break somewhere, but knowing what should be hot at the ECM side would help me get this sorted out. Thanks in advance.

 

[LoggNM]

I ended up purchasing a diagram for this model - may be slightly different for different models and engines.

On the 2011 Yukon Denali with the L94 6.2 AFM Flex Fuel motor, the IAT is integrated with the MAF and there are two separate wire connections between the sensor and the ECM X1 connector:

Pin #37 (Tan/Blk) goes to Pin B of the IAT/MAF Connector (also Tan/Blk) Circuit 472
Pin #38 (Tan) goes to Pin A of the IAT/MAF Connector (also Tan) Circuit 2760

These wires are bundled into the engine harness from the IAT/MAF connector (intake pipe right front of engine bay) back under the Coolant Overflow Tank and Battery tray, then up and over the right side firewall, then forward and up over the back of the intake, then branching at the top of the intake downward to the main harness ECM connector on the left front of the engine bay. Tracing these wires looks relatively accessible, but there are multiple tan wires so it'll take some care to trace .

Hope this info help someone else with an IAT Code P0113 that may be related to a wiring issue.