4x4 on chevy 2500HD duramax will not disengage

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

Wade Cook

• 6 Answers
• Posted on Jan 27, 2009

SOURCE: 4X4 inop on 2003 GMC Sierra 2500HD

I have found that when you are going to engauge 4x4 high, it is best to only be going about 3 miles an hour. Not faster, not stopped. It likes some movement to help it mesh. I've had perfect shifts since I started this. Hope it helps. Wade.

SOURCE: 2005 chevy 4x4 6.6 duramax

i have the same problem... its the guage cluster..apparently there was a recall on this from 03 to 05 models...i may think u need a new cluster..hope this was helpful..

Roy Funkhouser

• 140 Answers
• Posted on Aug 28, 2009

SOURCE: Need to know Oil Capacity for Duramax 6.6 in 2004

Hello,
The requirement is 10 QTS. I use 10 and check it cause some times they hold 11 QTS. I hope this helps. If you have more questions reguarding this or other conserns please ask me. Please remember high ratings are very important to me.

Thank You,
Roy

Testimonial: "Thanks very much for that Regards Bryan McRae New Zealand"

SOURCE: 2002 chevy hd duramax 4x4

Sounds like the PRNDL switch on the side of the transmission. Be sure and clear the code before trying to start after replacing it.