Ok, the P0102 was pretty straightforward... The MAF sensor wiring came loose from the sensor.
In these cases, you should always check to make sure there is enough slack in the harness; the
torque of the engine may be pulling the wiring from of the sensor. In this instance, there was plenty
of slack.
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The P0102 Failure Record has been updated since its first failure. We know that by looking at "Miles Since First Failure" and "Miles Since Last Failure". We know that the first failure was 3 miles ago and that the diagnostic has failed 4 additional times since the initial failure 3 miles ago. We also know that the diagnostic has not passed a single test since the first failure. That is good, we hate intermittents... Now, we do not know the P0102 diagnostic conditions for the previous 4 failures, but we do know the conditions on the last. Seeing that the engine was not running at the time of the failure, we can assume that the PCM wants to see SOME MAF input on key up. If you see ZERO g/s, then there is a problem. |
You might think we just wasted a lot of time going over obvious stuff, but I think that Freeze Frame
and Failure Record data is often informative when you stop and take a good look at it. Consider
making it a habit to try and figure out what the engine and driving conditions were at the time of the
data recording.
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Ok, moving along to the trouble maker... the P0446... In a nutshell, the failed diagnostic means that the PCM thinks that the Evap system cannot vent at all, or fast enough. It's really that simple. Enable criteria? Who cares! Look what I know from the data... • The last P0446 diagnostic failed • It has both passed and failed since initial fail • The first failure was 412 miles ago • The last failure was 3 miles ago • Since the initial failure, the P0446 diagnostic has run 7 times and only failed twice |
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Looking at the snapshot plot, we can see that the system is now venting properly. So what do we do? This is where I like to have fun with the OEM types... I'll tell them that I will make a guess and blow it out of here! I'll sneak under the truck, make sure that all the vent lines are in good shape (not kinked etc...), check vent solenoid wiring, check briefly the tank pressure sensor wiring, and then throw a new Vapor Canister on it. Run the monitors afterward? Are you crazy? It only pays 2/10 for the whole job! No, they do NOT pay ANY diagnostic time for the failed canister... Nice people... |
It is not uncommon for carbon particles to come loose within the canister and create havoc with the system...
There is also another possibility; faulty prom calibrations <g> I always check, because if I can find an
update, it pays well to do it <g> Now don't read this and throw vapor canisters on any vehicle you find a P0446 on; just
keep in mind WHY this code sets and consider all the possibilities. Then track them down... Let the experts
worry about enable criteria; lets make some money..
In the future we will take a good look at the GM Evaporative systems and consider how
the PCM monitors for system degradation or failures.
!! IMPORTANT UPDATE !!
There is now a prom update that corrects the P0446. The original calibration did not allow enough time for the canister
to vent completely. Replacing the canister was a temporary fix, but the only one available to us at the time.