User`s guide

4 April 2012
What’s the cost of not following the proper diagnostic
procedures? In one case, a new transmission.
Strategy-Based Diagnosis has been emphasized for a long
time. A recent real-life example illustrates what happens when a
technician doesn’t perform Step 5 – Check for related Bulletins,
Recalls and Preliminary Information (PI), or when that information
isn’t followed or is disregarded.
A 2011 Avalanche was brought in to a dealership with an illumi-
nated Check Engine light and an erratically shifting and jerking
transmission.Thisvehicleisequippedwitha6L80automatic
transmission.
After a road test, the technician found that the line pressure was
erratic. He then dropped the transmission pan and, during inspec-
tion, found that the transmission fluid filter was split along the
seam. The filter was replaced and the transmission was refilled
with fluid.
When the vehicle returned with the same condition, the filter was
replaced again. After calling TAC and getting additional informa-
tion (#PI 0488A) about inspecting the pump when a cracked or
split filter is found, the filter was replaced once more; this time
with an aftermarket filter.
#PI0488A covers a no forward, no reverse or slipping condi-
tion on the 6L80 and 6L90 6-speed automatic transmission on
some 2010-2012 CTS V, Escalade models, Avalanche, Camaro,
Corvette, Express, Silverado, Suburban, Tahoe, Savana, Si-
erra, Yukon and Yukon XL models. It points out that if the filter
is cracked or split, the fluid pump should be disassembled and
inspected for possible damage, such as a scored pump rotor
or pump vanes, scored pump cover or pump rotor pocket, or a
cracked pump slide. The transmission also should be evaluated for
any possible distress to the clutches.
Upon inspection, the first, and obvious, repair is to replace the
damaged filter. The second, and less obvious, repair is to inspect
the pump. But if information in a PI doesn’t make sense, it should
not be ignored, which in this case, it was.
The damaged pump can send a high pressure fluid spike down
the filter neck on a cold start, resulting in the filter body cracking
or the filter seam splitting. The filter itself is not defective. If the
damaged pump isn’t replaced in time, it can lead to clutch damage
due to low line pressure and possible transmission replacement.
After a total of four filter replacements and further road testing, a
replacement transmission was ordered. Had the technician done
the proper Service Information research when the first damaged
filter had been found, even if the information in the PI didn’t ap-
pear to make sense at first glance, following the PI and checking
thepumpwouldhaveleadtoaquickandcorrectrepair.Repairing
the pump would have been much less expensive than replacing
the transmission.
The final result of this repair is that GM did not pay for the
transmission replacement. It was a costly mistake and an
unnecessary repair.
Remember to follow Strategy-Based Diagnosis and check
the Service Information for the latest Bulletins and PIs. These
resources have been put in place to help avoid expensive and un-
necessary repairs that waste technicians’ time, lead to needless
parts replacement, drive up warranty costs, and cause customer
dissatisfaction.
Thanks to Dave Peacy
The Cost of Not Doing Your Homework
Duramax Diesel Exhaust Gas Temperature Sensor
Four Reading Incorrectly
During normal diagnosis of a 2011-2012 Express, Silverado, Sa-
vana,orSierraequippedwiththe6.6LDuramaxdieselengine
(RPOs LGH, LML), it may be noticed that the Exhaust Gas Tem-
perature sensor four (EGT 4) is reading incorrectly. This may be
noticed with or without any EGT DTCs.
If a 2012 model year vehicle is inadvertently built as a 2011 model
year vehicle, some of the data parameters on the Tech 2 may be
incorrect. If this is encountered, make sure all the vehicle identifi-
cation information has been input correctly.
A2012diesel-equippedvehiclebuiltasa2011vehiclewillshow
EGT 4 at or near 1000° C/1850° F. If a reading of 1000° C/1850°
F has been found on EGT 4, do not replace the sensor until after
checking that the vehicle is built correctly on the Tech 2.
If an incorrect reading is found, and the vehicle identification has
been input correctly, continue with the appropriate Service Infor-
mation diagnostic for the symptom or DTC.
Thanks to Donald Langer
Spilt transmission fluid filter caused by a damaged pump