Nissan Maxima's Burning Bush
Robo Tech was called to a repair shop on a Nissan Maxima, with a 3.0 liter engine, experiencing
a low or high idle condition. It was also accompanied by a check engine lamp on, with
a code P0 505, or Idle Air Control System Malfunction. The repair shop performed a throttle
body cleaning and replaced the spark plugs, which were severely worn out. They also tested
and replaced the throttle position sensor, but none of these measures solved the problem.
The erratic idle continued, and it was then that the shop decided to call me in for assistance.
I started my diagnostics by scanning the vehicle’s E C M, and see what it perceived. A scan tool,
is a window into the E C M, and sure enough, code P0 505 came to view. Ok, this was expected
and not out of the ordinary. I then decided to perform a bi-directional control of the
idle control valve, which was a fully motorized unit, using 4 coil windings. As I performed
the bi-directional control, nothing happened. The valve was totally out, either due to the
E C M, not commanding or the valve itself. The bi-directional control forces the E C
M into performing an action.
My next diagnostic path was to grab a multi meter, or in my case, a graphing multi meter
and test for idle control valve resistance. I removed the I A C valve, and checked for
more than 20 Ohms resistance. If they were, them the idle control valve was shorted. All
four coils on the I A C valve tested fine, so I next easily re-installed the valve. My
next move was to check the command signal to the I A C valve.
I connected the graphing meter to the coil output, and using the scan tool, commanded
the idle control valve to a higher and lower percentage. As I did that, I saw no change
in the graphing multi meter. Ok good, so my issue was at the command wires, or the E C
M was not actuating the I A C valve.
I was getting close to the problem. I reasoned, that the issue was probably in a broken wire
to the I A C valve. As it turned out, the E C M, where the wires come out of to the
I A C valve is buried in the center console on most Nissans. Removal of the E C M would
take too long. So, I opted for the fastest way to track a broken wire. I decided to connect
the fox and hound, tone generator to one of the I A C coil wire pair. This would introduce
a tone, and I could track through the insulation and wire tubing. As I proceeded to track for
the broken wire, and entered the inside of the vehicle, close to the center console,
I could smell a slight burnt odor.
Ok, this was starting to get hot! What could possibly have caught on fire?
For the first time I started to suspect the E C M itself. The tone tracking led me right
to the E C M connector. I did the same wire tracking test, on all four, idle control coils.
The wiring was sound and without issues.
I knew that the E C M most likely got damaged. I then, after some work, removed and opened
the E C M to inspect for a burnt I C chip, on the circuit board, but what a shock? I
did find a rectangular upright chip that was totally fried. As soon as I opened the E C
M, I was able to smell the strong burnt odor. I instructed the shop to replace the E C M
and the vehicle issue was never seen again.
I later did some research to see if this was a recurrent problem, and found that, sure
enough, this was happening more often than not. There were no technical service bulletins
for the matter, which goes to show, that service bulletins are not necessarily expected. This
case, shows that through proper diagnostic procedure, you’d surely find
your problem.