4L8OE tranny troubleshooting.

REPORTS FROM SWA INDICATE THAT SOME DRIVERS AND UNIT MECHANICS DON'T QUITE UNDERSTAND THE OPERATION AND TROUBLESHOOTING OF THE 4L80E TRANSMISSION IN ALL M998A2-SERIES AND UP-ARMORED HMMWVS.

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JUST ABOUT EVERYTHING UNIT LEVEL OPERATORS AND MECHANICS NEED TO KNOW ABOUT THE 4L80E CAN BE FOUND IN TMS 9-2320-280-10 AND -20-1 AND TMS 9-2320-387-10 AND -24-1.

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OPERATORS, WHEN THE TRANSMISSION WILL NOT SHIFT INTO THIRD GEAR AFTER REACHING ABOUT 35 MPH, DON'T EXCEED 35 MPH AND GET YOUR TRUCK TO YOUR MAINTENANCE FACILITY ASAP.

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MECHANICS, WHEN A DRIVER TELLS YOU ABOUT THE TROUBLE MENTIONED ABOVE, GO DIRECTLY TO SECTION 2-35 OF THE -280-20-1 TM OR SECTION 2-40 OF THE -387-24-1 TM (OR FIND BOTH IN ETM 0030).

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EVERYTHING YOU NEED TO TROUBLESHOOT CAN BE FOUND IN THESE SECTION.

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You will also need some special tools noted in the TMs:

* Diagnostic switch cable, NSN 6150-01-410-8215

* Throttle position switch (TPS) cable, NSN 6150-01-412-7774

* TPS block gauge, NSN 4820-01-179-4869

HERE'S SOME EXTRA INFO ...

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If a HMMWV with a newly installed transmission goes into "limp mode" (won't shift out of second gear right away, it could have the wrong erasable programmable read-only memory (EPROM) chip installed. 1995 and 1996 Model 4L8OE transmissions require EPROMS that are matched to the model year of the transmission. 1997 and newer transmissions can use the latest model of EPROMs.

For training or assistance to troubleshoot the 4L8OE transmission, contact your local TACOM logistics assistance representative (LAR).