having a problem with pcm or ecm what ever you know this part by , basicly
the computer. funny story i had the shocks changed and the so called
profecional left the wiring for the intake air temp. sensor haning on the
a/c bracket. anyway they got caught in the fan and shorted somthing out.
i ran the codes and it came up code 25 short on the IAT sensor circuit.
the sensor is fine but the truck is running realy roughand check engin
light is on. so my question for any one up to the chalange is 1.is there
an external resistor, relay, breaker befor the pcm 2. is the resistor in
the pcm, 3. and finally why the hell is gmc dealer ships full of brain
i wish it were that easy but i think the guy would do more harm than good.
i checked part of the wire for voltage before the fire wall and at the
sensor conection, ive also replaced the ecm and it helped a little but
the check engin light is still on. after it comes past the fire wall it
is so tight that its hard to tell were every thing is going so i wired the
line up so i could check for continuity but ive had no luck this leads me
to belive that it must pass through something before the ecm. if any one
knows how to get some wireing diagrams of the iat senror circit that would
Assuming you have the L4 engine:
The IAT signal comes from the PCM at terminal B9 (TAN) and goes directly to
the sensor (terminal A). From the sensor, a BLK wire (terminal B), is
spliced directly into the MAP sensor terminal A wire (BLK) and then to the
PCM terminal B4 (sensor ground).
Replacing the PCM is more often than not nothing but a placebo. If the MIL
is still on, replacing the PCM didn't fix anything.
That being said, this particular code will cause the MIL to stay on until
the codes are cleared or the ignition is cycled 50 times with no fault.
Clear the codes and see if it comes back.
What I would do is disconnect connector B from the PCM, disconnect the MAP
sensor and the IAT sensor. Then check for a short to ground on B4 and B9. If
that checks out, check for continuity between terminal A (IAT) and B9 (PCM).
Then check for continuity between terminal B (IAT) and terminal A (MAP).
Then between terminal B (IAT) and terminal B4 (PCM).
Also check to see if the IAT sensor is shorted to ground, there should not
be continuity between either terminal on the IAT and ground.
That's a good start.
no luck this is what ive done, there is no short to ground on the iat
termenels, there is continuity between iat and map ground, the voltage on
the map is 5 volts, there is 5 volts on a9 terminal going into the pcm,
and i did this with bolth new and old pcm(as much as i could some parts
were not hoohed up for the tests oviously)
You still have to check for short to ground on the signal wires. The DTC you
are getting is a low voltage code, so you really have to check for a short
to ground on the signal. Also, clean the PCM connectors. If all checks out,
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