jhanson450

I have a 98 trans am with an 03 lq4 that I'm trying to get running right so I can learn how to tune with hp tuners. Right now I'm trying to figure out what's wrong with the iat sensor. On the scanner I'm showing -38 degrees even with new sensor. So I cut the connector off and jumped the two wires together and it moved to -36 degrees. I am getting 5 volts from both wires when I use a chassis ground which I read (but doesnt sound right) meant a break in the ppl ground wire to the PCM. I checked continuity from pin 21 (98 ls1) on my PCM to the end of the ppl wire where the connector would be and my digital meter changed from 1 to .000 (infinite) but when I check continuity from ppl wire to chassis ground I get no change. So now im hoping someone else can PLEASE help me out cause I have no idea where to go from here???

jhanson450

Also checked pin 72 (PCM ground) to a chassis ground and got .000 on my volt/ ohm meter. I am thinking for sure I have a bad ground somewhere cause I have a p1539 (a/c something high voltage) and another code for high voltage with something with the fuel tank..... All the high voltage codes would mean a bad ground somewhere right??

2xLS1

iTrader: (25)

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jhanson450

So both wires run straight to the PCM?? My PCM ground has continuity to the chassis ground but my ppl iat ground has 5 volts for some reason also with good continuity to the PCM but no continuity to a chassis ground

gagliano7

Going by that drawing the purple wire should be a ground and tan wire should have voltage.

jhanson450

Yea but they both have 5 volts and I'm trying to figure out why. I have continuity from end of ppl to PCM and continuity from both PCM grounds to chassis ground but not from end of ppl to chassis ground..... Does something else tie into this equation somewhere?

How many chassis grounds are on our cars? Maybe I should clean all of those up real good?

MontecarloDrag

iTrader: (3)

If both pins at the sensor have 5V, then the pink wire must be broken.

jhanson450

Go ahead and call me a slacker cause I haven't even checked that wire for continuity to the PCM.... It does run straight to the PCM though right?? I will be checking it in a few hours when I get off work. Thanks

jhanson450

Ok. Good continuity between ppl to PCM, tan to PCM, both PCM grounds on blue connector, AND both grounds on red PCM connector.… I'm stumped! C'mon guys I know somebody knows something??? Does this tie in somewhere else? I can't tune my new 6.0 until I get this right. I also am throwing these codes: P0113, P0405, P0463, P1111, P1539, P0300
The p0300 is from my cam and not having it tuned and I left the egr and air pump stuff off

MontecarloDrag

iTrader: (3)

Yes both wires go straight to the PCM, nothing else is hooked to them.

I'm thinking a bad sensor or damaged connector. Check connector's pins, sometimes they get pushed and don't make contact with the sensor.
Unplug it and check sensor's resistance. It should read like 2000 Ohms at ambient temp. Since it's always reading -38 deg I think the sensor is open, so the PCM sees infinite resistance and uses the lowest temp in the IAT table.
If you get infinite resistance or a short at the sensor pins then the sensor is bad.

With ignition key open, unplug sensor and short both pins at the connector using a paper clip. In the scanner you should see like 300 F.
Buy a 1 Kilo ohm resistor and plug it to the connector, you should see like 120 deg F.
With harness unplugged you should see -38 deg.
If the 3 tests give you similar results then the PCM and harness are OK. If they fail you have a faulty PCM or wiring.

jhanson450

I have faulty wiring somewhere... I cut the pigtail off so I've been checking from the ends of the bare wires. Touching them together only moves temp from -38 to -36 for some reason. Next time I get in the garage I'm gonna wiring to PCM power and see if I can figure out the a/c clutch high voltage problem and the fuel tank level high voltage problem and maybe they will cure the iat high voltage problem...
When I finally figure it out I will definitely post it on here cause I've read I don't know how many posts and can't find a problem like mine that was resolved

joecar

Follow the diagnostic procedure here: http://www.gearchatter.com/viewtopic8762.php

jhanson450

Ok I found that I have a bad ground by running a jumper from the iat pigtail (ppl) to a chassis ground.... It shows 72 degrees now on the scanner but I hate to leave it rigged up like that. I have checked continuity to the body and the head on all four PCM grounds and checked the voltage to the b+ and they check out good. My fuel gauge is also showing empty cause of (assuming) bad ground to the fuel level sender causing the high voltage dtc to set. Does anyone know which ground I should check??? Or maybe it's a certain relay? I am so confused and frustrated right now. Lol but i know I'm almost there so any input will be highly appreciated