Old School OBDII - EGR Flow Test - Aftermarket Parts

Scott Owner/Technician Claremont, California Posted   Latest  
Case Study
Driveability
Emissions
1998 Chevrolet Camaro 3.8L (K L36) 4-spd (4L60-E)—2G1FP22K9W2117298
P0401 - EGR "A" Flow Insufficient Detected
P1404 - Egr Closed Position Performance

For anyone interested in seeing an early GM OBDII diagnostic routine in action, check out this video case study. It's not cutting edge, but it does illustrate how much data GM provided technicians way back in the early days of OBDII.

This tale was worthy of a case study in my book because what should have been a slam-dunk service, turned into a multi-visit comeback. Hopefully it might help someone in the future. Fortunately, this was a long time customer with a vehicle we've been taking care of since she bought it new.

The vehicle initially arrived with a P1404 and if you're still reading, watch the video for the rest of the story.

For reference, this is what the PCM runs for diagnostics on the P0401 according to SI:

CIRCUIT DESCRIPTION The PCM tests the EGR system during deceleration by momentarily commanding the EGR valve open while monitoring the Manifold Absolute Pressure (MAP) sensor signal. When the EGR valve is opened, the PCM should see a proportional increase in MAP. If the expected increase in MAP is not seen, the PCM notes the amount of error that was detected and adjusts an internal fail counter towards a fail threshold level. When the fail counter exceeds the fail threshold level, the PCM will set DTC P0401. The number of test samples required to accomplish this may vary according to the amount of detected flow error.

Normally, the PCM will only allow one EGR flow test sample to be taken during an ignition cycle. To aid in verifying a repair, the PCM allows a specified number of test samples during the first ignition cycle following a scan tool Clear Info or a battery disconnect. Between nine and twelve samples should be sufficient for the PCM to determine adequate EGR flow and pass the EGR test if the system is operating correctly.

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G Educator
Mahopac, New York
G Default
 

Scott nice job ...its good to see you in a uniform again 😉

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Scott Owner/Technician
Claremont, California
Scott Default
 

On top of that, it still fits! Thanks G

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Kevin Manager
Leesburg, Virginia
Kevin Default
   

Nice video Scott. I had a similar experience with this aftermarket parts supplier. I installed a new fuel tank module in my daughters car as PM. The original fuel pump had over 150K and I knew it was a matter of time. Because my daughter is going to school out of state, it seemed like a responsible thing to do. The car worked fine for a few weeks then EVAP leak DTC. Every time I ran the…

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Scott Owner/Technician
Claremont, California
Scott Default
 

Thanks for sharing your story. Folks making these deficient parts don't quite realize the grief they inflict!

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Scott Owner
Moreno Valley, California
Scott Default
 

Hi Scott, Nice video and you did a good job on describing the problem. I'm also a proponent of taking snapshots and analyzing the data to determine the fault. I do have a couple of questions on why you chose to use EFI Live instead of the Tech 2? I'm not familiar with EFI Live, so...Is the update rate faster than the Tech 2's, which I believe is 200 ms? Is it the limitation of the Tech 2 only…

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Scott Owner/Technician
Claremont, California
Scott Default
 

Hi Scott, The Tech2 snapshot and replay function didn't allow me to scrub through the data and measure the difference very cleanly. The update rate is dependent on the vehicle controller and yes, 5 times/sec. Some of the newer controllers are much faster. The other downside you mentioned is the snapshot function. When they were engineering the Tech2 I would venture to guess that they didn't…

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Scott Owner
Moreno Valley, California
Scott Default
   

Hi Scott, Thanks for the link. Yes, Jim and some others, were part of the reason I started taking snapshots and using them for diagnosis. I've had some conversations with Jim, and as you stated he went up against a brick wall with GM, trying to get some of the bugs and limitations worked out with the snapshot and display functions for the Tech 2. Essentially it boiled down to this works well…

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Michael Technician
Amherst, Massachusetts
Michael Default
 

Thanks for sharing your great case study Scott !! And thank you for your support of TST seminars.

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Scott Owner/Technician
Claremont, California
Scott Default
 

You’re welcome Michael, and I’m happy to help support the TST folks helping move the industry forward!

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