A/T - Slow/No Gear Engagement/Engine No Start
Bulletin No.: 02-07-30-011C
Date: June 21, 2004
TECHNICAL
Subject:
Slow or No Engagement of Automatic Transmission, No Start, Blank PRNDL Display, Flashing PRNDL, DTC P0708, P0872, P0847, P0875, P1711, P1713 or U1000 Set (Diagnose Condition, Repair According to Procedure)
Models:
2001-2004 Chevrolet Silverado
2001-2004 GMC Sierra
with Allison(R) LCT1000 Automatic Transmission (RPO M74) and
6.6L Duramax(TM) Diesel Engine (RPO LB7) or 8.1L Gas Engine (RPO L18)
Supercede:
This bulletin is being revised to add model years and additional model information and add graphics. Please discard Corporate Bulletin Number 02-07-30-011B (Section 07 - Transmission/Transaxle).
Condition
Some customers may comment on one or more of the following conditions.
^The PRNDL display is flashing.
^The engine will not start.
^The "Service Engine Soon" Indicator lamp is illuminated.
^The transmission does not shift properly.
^The vehicle will not move, transmission will not engage.
Cause
Moisture contamination within the Park Neutral Position switch may cause this condition. This is sometimes referred to as the Neutral Start Back-up (NSBU) Switch. On a left turn, water spray from the left front tire is directed directly at this switch. Proper installation of the "Front Shield" and "Rear Shield" are essential for proper repairs.
Technician Diagnosis
This bulletin ONLY applies to vehicles equipped with a two connector PNP switch as shown above.
A complete and through diagnosis must be performed by a qualified electrical technician to determine the cause and avoid needless replacement of good components.
Important: The Transmission Control Module (TCM) and or the Pressure Switch Manifold (PSM) should NOT be replaced unless properly diagnosed. They are probably not the cause of the concern. It is often assumed the module is the cause of the concern when, in fact, it is another component or the wiring between the components that causes the concern.
Important: Remember, everything starts with a properly operating Neutral Start Back Up (NSBU) switch. The NSBU switch has been incorporated into what is now called the Park Neutral Position (PNP) switch. If the PNP switch does not provide the proper voltage signal to the module indicating the transmission is in either Park or Neutral, the module will not allow the starter operation. After the engine is started, and the shift lever is moved to either Reverse or one of the drive positions, the range selected portion of the PNP switch portion provides a voltage input to the module as to what range the driver has manually selected for transmission operation. The module then controls pressures, shift points and other transmission functions based on the voltage input received from the range portion of the PNP switch.
The technician may find one or more of the following conditions. The list of these conditions does not imply any type of frequency or order. They are random events and may occur in any order.
^DTC P0708, Neutral start/backup (PNP or NSBU)
^DTC P0847, Pressure Switch Manifold (PSM)
^DTC P0872, Pressure Switch Manifold (PSM)
^DTC P0875, Pressure Switch Manifold (PSM)
^DTC P1711, Pressure Switch Manifold (PSM)
^DTC P1713, Pressure Switch Manifold (PSM)
^DTC U1000, Serial Data Communications
^Blank PRNDL Display
^Flashing PRNDL Display
^Slow or No Engagement of Automatic Transmission
Or, a blank PRNDL display may also occur if an out of line condition exists with the Serial Data Circuit (CKT 2470, yellow wire) from the TCM to Splice Pack 205.
Diagnostic Tip
1.Connect the Tech 2(R) to the vehicle.
2.Power up the Tech 2(R).
3.Does the Tech 2(R) communicate with the TCM? If not, inspect the serial data circuit, CKT 2470 (Yellow wire), between the TCM and Splice Pack 205. Specifically inspect connector C106, a five terminal connector located below the left side underhood bussed electrical center, directly beneath the red battery cable terminal connection. Perform a mating terminal pull test on all of the terminals in this connector. Repair as required.
4.Observe the Gear Selected screen on the scan tool. The following values should be shown on the Tech 2(R) display and the vehicle's instrument panel cluster (if equipped with the I/P display).
^"8" (shifter should be in the Park position)
^"7" (shifter should be in the Reverse position)
^"5" (shifter should be in the Drive position)
^"3" (shifter should be in the Third gear position)
^"2" (shifter should be in the Second gear position)
^"1" (shifter should be in the First gear position)
^"0" (shifter should be in the Neutral Position)
If the Gear Selected display does not match the shifter position in the vehicle, diagnose using one of the following methods.
^Obtain a new PNP switch kit, P/N 29540479, from the Parts Department.
^0.1. Disconnect the wiring connector from the original transmission mounted PNP switch.
^0.2. Connect the new switch to the wiring connector.
^0.3. Return to Step # 4 above and observe the display as you rotate the switch. If all positions indicate properly, refer to the Correction section below.
^Use the DTC P0708 diagnostic chart in Service Information (SI) under Transmission/Transaxle/Automatic Transmission
-Allison. Reference SI Document ID # 769549 for the wiring schematic for this symptom.
The PNP switch, as referenced in SI, is known as the NSBU switch in the Parts information. It is now serviced with a Park Neutral Position Switch Kit, P/N 29540479.
Flashing PRNDL Display
A flashing PRNDL display may be the result of incorrect sensor inputs or transmission abuse protection modes being received by the TCM. The following are some of these conditions:
^The transfer case is/was in Neutral.
^The transfer case is/was shifted into Neutral when the vehicle is moving.
^A decrease of the input turbine speed was not detected when the gear selector was moved into any gear.
^A low transmission fluid level.
^A misadjusted PNP/NSBU.
^Turbine input speed or output speed sensor failure.
^Failures of the shift solenoids to route the transmission oil to the proper clutch assemblies within the transmission.
^Failures of the transmission clutch packs (C1 or C5 for first gear, C3 or C5 for Reverse).
^Failure to detect proper line pressures when a gear range is selected, which may be the result of normal maintenance such as a transmission fluid change having been completed, or the transmission pan was removed for a filter replacement or other type service.
