Here's the story... My girlfriend is the main driver of my Blazer. She has told me about an issue with the trans shifting hard sometimes, but it comes and goes. I have NEVER felt it shift rough anytime that I've driven it even when pulling a little weight. I have also had a CEL that was a P0442 code. I replaced the gas cap and it's now intermittent. Recently, the trans has developed a constant harsh shifting issue. The CEL is on for good now so I went to Autozone to get the codes read.

Here are the codes that came up:
P0740- TCC enable circuit
P0442- EVAP small leak/ no flow condition
P0107- MAP/BARO or MAF/VAF sensor condition
P0102- MAP/BARO or MAF/VAF sensor condition
P0113- IAT circuit
P0172- Fuel trim bank one condition
P0175- Fuel trim bank two condition
P0306- Cylinder misfire detected-cylinder #6

As far as the trans issue goes, my plan was to replace the trans valve body and a fluid/ filter change. That should clear up any current or near future failures with that(as long as the clutches are in good shape). My big question is what about the rest of the codes? Are there any tests I can do to find exactly what the failures are? I have access to a tech2 scan tool from work if that will help me... Excuse me for being a little illiterate on diagnosing gas engines. I am a diesel tech and work on Class 8 trucks(semis, big rigs, etc.). Thanks in advance!

 

for the maf codes pickup a can of maf cleaner,dont use brake cleaner. If you remove the square silver thing on the air hose to the engine and look inside you'll see a tiny sensor. spray it down and let it dry. dont touch it with anything but the spray. that might take care of the misfires and fuel trim too. pull of the iat as well. That should be a sensor screwed into the air hose too. clean it with the maf cleaner as well. pull the power off the battery,let it set for 15 min then start it and drive. see if anything comes back. Not sure on the trans problems.

 

Sounds to me like the typical bad ignition switch:
https://blazerforum.com/forum/articl...-switch-33465/

 

Captain Hook- Sorry for being lazy, but it's late and I don't feel like reading a whole thread.... Which issue are you referring to being related to the ignition switch? Also, why would you suspect the ignition switch?

Chris- I know how to clean a MAF... Like I said I am a technician, just in the diesel field. I have recently cleaned the MAF, but will do it again to see if it makes any difference.

 

The P0442 is probably legitimate because you had the problem before, however: The DTC's that you listed are all inputs to the PCM, (with the exception of the P0306 which may have been set eroneously when the other sensors malfunctioned). The one thing they have in common is the ignition switch. They get their voltage from different circuits out of the ignition switch. Ignition switch failure is quite common, and when it messes up, you end up with a whole string of DTC's, classic symptom. It's doubtful that it's a ground problem but those inputs use different grounds and you'd have other electrical issues if that were the case. I would suggest clearing all memory files, (pending, current, history, & fuel trims) with a scan tool. Disconnecting the battery will not clear the memories. Then perform a General Motors Driving Cycle. Do each step exactly as outlined. This forces all monitors to run and complete their tests. Then check readiness status to make sure all monitors are complete. Then retrieve any DTC's and post them here. In the link there is a schematic of the ignition switch, testing each circuit may reveal a problem too.

 

Thanks for the info! I'm guessing that I can clear the memory files with a Tech-2? Would I be able to run the entire GM Driving Cycle on jackstands or does there have to be a load on the driveline(actually driving on the road)?

Also, what do you think about my plan to go ahead and replace the trans valve body, fluid, and filter? Are there any other quick tests I can do before just wasting money?

 

Tech2 is the "GM dealer issue" scan tool, it is capable of clearing all memory files. Drive cycle needs to be done while driving, not on jack stands. As for transmission, best to diagnose & repair the driveability issues first, then diagnose the transmission.

 

Well I guess I better find me a long, unused back road lol. Dealerships can actually do this? Like, even the ones in the city?

 

To ensure all monitors run and complete their test, each step needs to be performed exactly as written in the drive cycle. The steps do not need to be done in order, or even on the same day, but they all need to be done to complete all monitors. If you only need to complete a certain monitor, (ie to verify a repair) you can perform the appropriate single step. With some practice, and some careful planning, the entire drive cycle can be done in about 15 minutes.