My 2002 2500HD Silverado diesel wont engage the front wheels in 4wd. I jacked the front wheels off the ground and put it in 4wd. The wheels turn and so does the front drive shaft. I found this out when I got stuck in the mud. I'm told that there is a 4wd electronic module on the transfer case that probably went bad? Does that sound logical and is this something easy to test and replace?

Evan Jenson

• 122 Answers
• Posted on Nov 05, 2008

SOURCE: replacing starter 02 silverado 6.6

1. Remove or disconnect the following:
   • Negative battery cables
   • Right front wheel and fender splash shield, on 6.6L engines
   • Turbocharger exhaust pipe, on 6.6L engines
   • Mounting bolts/nuts and shim, if used
   • Starter
   • Wires
   • Heat shield and bracket Exploded view of the starter motor-6.5L engine shown

1. Install or connect the following:
   • Heat shield and bracket. Torque the bolts to 13 ft lbs. (17 Nm).
   • Wires.Torque battery wire nut to 89 inch lbs. (10 Nm), and ignition nut to 18inch lbs. (2 Nm) on 6.5L engines. On 6.6L engines, tighten the solenoidnut to 30 inch lbs. (3.4 Nm) and the positive battery cable nut to 80inch lbs. (9 Nm).
   • Starter
   • Mounting bolts/nuts and shim,if used. Torque the bolts to 33 ft lbs. (45 Nm) and the nut to 75 inchlbs. (8.5 Nm) for 6.5L engines. For 6.6L engines tighten the starterbolts to 58 ft. lbs. (78 Nm).
   • Turbocharger exhaust pipe, on 6.6L engines
   • Right front fender splash shield and wheel, on 6.6L engines
   • Negative battery cables

SOURCE: CHEVY SILVERADO 2500HD DURAMAX DIESEL

DTC P1093
Fuel Rail Pressure Low During Power Enrichment



The engine control module (ECM) uses the fuel rail pressure (FRP) sensor to determine fuel pressure to the fuel injectors. This is then compared to the calculated target fuel pressure as determined by the ECM. The ECM adjusts the FRP by modulating the duty cycle of the control driver of the fuel pressure regulator. Injector pulse duration is determined by the measured rail pressure and the target injection fuel into each cylinder. If a sensor circuit malfunction is detected, or the commanded fuel injection pump flow is not within the proper range for a given engine load and speed, DTCs will be set.

DTC U1000 and U1255 Circuit Description Modules connected to the class 2 serial data circuit monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules. When a module receives a message for a critical operating parameter, the module records the identification number of the module which sent the message for State of Health monitoring. A critical operating parameter is one which, when not received, requires that the module use a default value for that parameter. When a module does not associate an identification number with at least one critical parameter within about five seconds of beginning serial data communication, DTC U1000 or U1255 is set. When more than one critical parameter does not have an identification number associated with it, the DTC will only be reported once. The class 2 serial data line on this vehicle is a ring/star configuration. The following modules communicate on the class 2 serial data line:
• The body control module (BCM) • The digital radio reciever • The driver door module (DDM) • The electronic brake control module (EBCM) • The front passenger door module (FPDM) • The HVAC control module • The inflatable restraint sensing and diagnostic module (SDM) • The instrument panel cluster (IPC) • The memory seat module (MSM) • The powertrain control module (PCM) • The radio • The radio amplifier • The rear seat audio (RSA) controller • The rear seat entertainment (RSE) assembly w/U42 • The rear wheel steering control module • The remote playback device-CD player w/U1S • The transfer case shift control module • The transmission control module (TCM) w/Allison transmission • The theft deterrent control module • The vehicle communication interface module (VCIM) w/UE1

SOURCE: Transfer case leak

You mean between the case halves? It is just silicon, no gasket. These are good for the pump wearing a hole in the rear housing and leaking oil. The cure for it is a new rear housing and a piece called a case saver that keeps the pump from doing it again. Taking the transfer case apart to fix it is easy, I can tell you how to do it.

SOURCE: 99 Silverado 4-wheel drive not engaging

It does not seem that sufficient diagnosis was done. No, you cant give a specific diagnosis like that without tearing unit down. It's likely that they told you the most common failure and left it at that. Likely there is a problem with your unit...I think this becomes more of a trust issue than a mechanical one. A second opinion from an independent reputable shop may help but either way, you need to have it fixed. In not using it much, it makes me wonder how it got worn.
good luck

SOURCE: 1996 chevy silverado z71 electronic transfer case wont work

It's the transfer case vacuum switch. Easy fix.