ITT: you fix my Trailblazer

[MAY03LT]

So, you want to test your diagnostic and repair skills? Here is your chance!

You have the following items at your disposal:
-GM Tech2 scan tool
-OEM service information
-Nearly every tool that most DIY guys have, and a lot of tools that they don't have
-The internet, minus pay services like identifix and iATN
-A host of spare Trailblazer parts and special tools

In this case, the owner of this 2003 Trailblazer states that the SES light came on while driving. The owner reports no driveability problems, and has also stated that he made sure that the gas cap was tight before bringing it to you to be repaired.

You have verified that the SES light is on and it appears that the truck is running smooth.

What is your next course of action?

A: Pour fuel system cleaner into the tank
B: Scan the Powertrain Control Module for Diagnostic Trouble Codes
C: Replace the Mass Air Flow sensor
D: Hit up Wikipedia and study SES causes and theories




*This is 100% unscripted. I have no idea what is wrong with this truck and what the repair may consist of. I will try to update this thread every night around this time. Hopefully we'll all learn something, and of course, have some fun doing it.

 

[Blckshdw]

I say, get the code first, then research possible causes and theories for it.

 

[tricguy007]

I say trade it in for a newer one JK!!!!!! get me the codes

 

[blazinlow89]

I agree with Blckshdw, get the codes then research. In the time between research and diagnosis run the fuel system cleaner just for good measure.

Also is it a 5.3, MAF was not until later iirc?

 

[oh05ext]

codes first then gas can and a match

 

[TollKeeper]

I say, get the code first, then research possible causes and theories for it.

This, and also make sure that the wires for each of the coils is plugged in and tight.

 

[ScarabEpic22]

First, scan for codes.

Next, which engine? 03 could be 4.2L I6 or 5.3L V8 (LWB).

 

[TollKeeper]

Since the thread title is "you fix MY Trailblazer", I would have to assume he is talking about the 4.2 in his 03 model..

 

[gmcman]

Get codes.

Running smooth with no driveability issues..... but as a hunch...I say O2 sensor based on mileage.

 

[HARDTRAILZ]

B....Otherwise you are likely wasting money since codes are free

 

[The_Roadie]

Get the code, then PM The Roadie for the fix or to get him to do the searching and cough up the list of all possible fixes.

Spoiler

Happens so often it must be in an FAQ somewhere I don't know about.

 

[HARDTRAILZ]

Mr Roadie.. I uh well I found this red wire....

 

[MAY03LT]

Before you had a chance to scan the pcm, the light went out on it's own! WTF!

What do you guys suggest we do now?

Also, Erik this is a 4.2 I6.

 

[Matt]

Still look for stored codes.

 

[Blckshdw]

and if there's no stored code, wait for the CEL to come back on so you can pay closer attention to the driving conditions, speed, RPMs etc so you can try to replicate the scenario at a later time in case the light goes out again before you get your hands on the scanner again.

 

[ScarabEpic22]

Before you had a chance to scan the pcm, the light went out on it's own! WTF!

What do you guys suggest we do now?

Also, Erik this is a 4.2 I6.

Thanks, figured it was your 4.2 but cant hurt to ask.

Still look for stored codes.

This, the codes should still be in history for a certain number of key cycles (not sure what the limit is on our PCMs).

and if there's no stored code, wait for the CEL to come back on so you can pay closer attention to the driving conditions, speed, RPMs etc so you can try to replicate the scenario at a later time in case the light goes out again before you get your hands on the scanner again.

Yep, and check the freeze frame data when you stop, it will have all the info (RPM, speed, MAP, TP, etc) from the exact time when the CEL was thrown.

 

[floridarv]

Clean the throttle body....

 

[Ilikemy3s]

#1 .. turn the cruise control off ..(in picture) basically return to normal driving and see if light reappears ..

 

[MAY03LT]

You guys are good. You fired up your scan tool and this is what you got from the DTC section of the PCM. This is the only code in the PCM, as indicated by the 1/1 at the lower right of the screen.

What should we do now? There are many ways to go from here, so we'll narrow it down a little. We could....

A: Consult the OEM manual for P0442 troubleshooting
B: Test the Vent Valve by putting 12v and ground to it
C: Crawl under the truck and look for a leak
D: PM the roadie


*This is actually cool. I was hoping it wasn't something easy like a coilpack. Now we have an evap problem that's intermittent. Double cool and double hip.

 

[jailfood]

How long after you put gas in it did the light come on ?

Mine did this to me 3 or 4 times till I changed the gas cap.

 

[RedVirus]

check your gas cap or it could be the filler tube has a leak

 

[tricguy007]

Here's what ya do back out a screen or to till u find the functional test screen then u find the vent valve and power it on and off with the sccanner if it clicks its works(that doesn't mean it is sealing) , turn the valve on then u get a smoke machine hook it up and look for the smoke

 

[ScarabEpic22]

My 02's had that code for a year, now that it's back in Seattle Im going to get a new gas cap first (it's not clicking as solidly into place like it should) then look for the fuel neck leak. If that doesnt do it, it'll get a smoke check from a mechanic (not looking forward to paying someone to do this, my trucks dont go to a mechanic).

But from your list of options, look at the service manual. Or you could PM Bill and ask him if you should look at the service manual!

 

[djthumper]

Tighten the gas cap followed by replacing then A

 

[tricguy007]

Any good news yet

 

[Matt]

Remove gas cap. Replace gas cap. Clear code and see what happens. (Just did that last night to wife's Rav4 - CEL was on and I Torque'd it.)

 

[MAY03LT]

Well after 2 days flapdoodling around I give up trying to get good quality pics of the service info. Copypaste will have to do.

DTC P0442
System Description

This DTC tests the evaporative emission (EVAP) system for a small leak. The control module monitors the fuel tank pressure (FTP) sensor signal to determine the vacuum decay rate. At an appropriate time, the control module turns the EVAP canister purge valve ON and the EVAP vent valve ON. This allows the engine to draw a vacuum on the EVAP system. At a calibrated time, or vacuum level, the control module turns the EVAP canister purge valve OFF, sealing the system, and monitors the FTP sensor input in order to determine the EVAP system vacuum decay. If the control module detects a leak larger than a calibrated amount, this DTC sets.

The following table illustrates the relationship between the ON and OFF states, and the Open or Closed states of the EVAP canister purge and vent valves.

Control Module Command ON OFF
EVAP Canister Purge Valve OPEN CLOSED
EVAP Canister Vent Valve CLOSED OPEN

Conditions for Running the DTC

DTCs P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0122, P0123, P0452, P0453 are not set.
The ignition voltage is between 10-18 volts.
The barometric pressure (BARO) is more than 75 kPa.
The fuel level is between 15-85 percent.
The engine coolant temperature (ECT) is between 4-30°C (39-86°F).
The intake air temperature (IAT) is between 4-30°C (39-86°F).
The start up ECT and IAT are within 9°C (16°F) of each other.
The vehicle speed sensor (VSS) is less than 121 km/h (75 mph).

Conditions for Setting the DTC

The EVAP system can achieve vacuum but a vacuum decay is detected during the diagnostic test.
Action Taken When the DTC Sets

The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

Conditions for Clearing the MIL/DTC

The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
Clear the MIL and the DTC with a scan tool.

Diagnostic Aids

To help locate intermittent leaks, use the J 41413-200 Evaporative Emissions System Tester (EEST) to introduce smoke into the EVAP system. Move all EVAP components while observing smoke with the J 41413-SPT High Intensity White Light.
To improve the visibility of the smoke exiting the EVAP system, observe the suspected leak area from different angles with the J 41413-SPT .
For intermittent conditions, refer to Intermittent Conditions .

So that's how the system works and what it takes to turn the light on, as well as turn it off, which is what happened in this case. If we go to the Intermittent Conditions section it tells us that we're screwed.

This is what we're told to check next. After this step, we need a smoke machine which I do not have. Firstworldprobems, ya dig?

Inspect the evaporative emission (EVAP) system for the following conditions:
A loose, missing, or damaged service port dust cap and/or schrader valve
A loose, incorrect, missing, or damaged fuel fill cap
A damaged EVAP purge solenoid
Raise the vehicle on a hoist. Refer to Lifting and Jacking the Vehicle in General Information.
Inspect the EVAP system for the following conditions:
Any disconnected, improperly routed, kinked, or damaged EVAP pipes and hose
A damaged EVAP vent solenoid or EVAP canister

It sounds like some of you guys have dealt with this darned evap crap before. If you were sticking to the script, and knew that the system test has passed since the code first set, which of the items in the list above can you rule out?

 

[tricguy007]

I would start with the vent valve then the gas cap(unless it has a cracked gasket) then look at the evap lines for and irregular signs of damage, a bad purge valve might throw a code for (excessive purge flow) then last I would check any connections on top of the gas tank including the fuel pump sealing ring for leaks( this one will be hard to do without a smoke machine)

 

[tricguy007]

I just remembered if u still have the TECH II you can force run an evap test (some times called a BAY TEST)in the functional tests screen

 

[Voymom]

I'm going to go out on a limb and also say the gas cap...Mat had an EVAP code, can't remember exactly what it was, but I think it's the same code as yours or similar. He has issues when he fills the gas tank completely, truck has stalled after complete fuel up's but not on partial's, and it runs perfectly fine afterwards too. He has an intermittent CEL as well, his light came on a few days ago, fueled the TB up, stalled at gas station, after a few cycles the light went off, no other symptoms of any kind either.

If it were me, and it was an option, I would start there. Can you rule it out by switching with another TB? I'm not familiar with the whole as cap thingy, except that it's a PITA to lock in place on Phantom.

 

[MAY03LT]

I just remembered if u still have the TECH II you can force run an evap test (some times called a BAY TEST)in the functional tests screen

Yeah you can do that. You can test purge and vent and watch the ftp sensor to see if it's all working, which it should be. Will update with results tomorrow or Sunday.

Seems like the gas cap is getting a bad rap here. You do have a good test cap that you can put on if you want to try it. If you bang that puppy on, how can you verify that it's the fix?