Powertrain Diagnosis

Circuit Description
The Powertrain Control Module (PCM) compares the measured gear ratio to the known actual value. This allows the PCM to determine the actual gear range of the transmission. When an upshift is commanded, the PCM measures the interval during which the gear ratio leaves the current range and changes to reflect the commanded upshift. This interval is expressed on the scan tool as Shift Time. When this interval has exceeded a predetermined limit, the PCM utilizes the shift adapts in order to attempt to shorten the shift time.

If the PCM detects that the maximum allowable shift time has been exceeded, and that the upshift adapts have reached their upper limit, then DTC P1811 sets. DTC P1811 is a type D DTC.

Conditions for Running the DTC
The engine must be running at greater than 475 RPM for more than 7 seconds.

Conditions for Setting the DTC
One of the following conditions exists, with the adapt cells at the maximum pressure allowed for 5 consecutive occurrences of one shift.
^ The 1-2 or the 2-3 upshifts are greater than 1.25 seconds.
^ The 3-4 upshifts are greater than 6.37 seconds.

Action Taken When the DTC Sets
^ The PCM does not illuminate the Malfunction Indicator Lamp (MIL).
^ The PCM freezes shift adapts.
^ The PCM commands maximum line pressure.
^ The PCM stores DTC P1811 in PCM history.

Conditions for Clearing the DTC
^ A scan tool clears the DTC from PGM history.
^ The PCM clears the DTC from PCM history if the vehicle completes 40 consecutive warm-up cycles without a non-emission-related diagnostic fault occurring.
^ The PGM cancels the DTC default actions when the fault no longer exists and the ignition switch is OFF long enough in order to power down the PCM.

Diagnostic Aids
^ DTC P1811 can be caused by a faulty turbocharger or wastegate assembly. If no other symptoms are present, check the turbocharger system for proper operation.
^ Ask the customer about overloading the vehicle, exceeding the trailer-towing limit, or towing in OVERDRIVE.
^ If, after several unsuccessful attempts to gain accurate shift times, and an adapt can be made, reset adapts and operate the vehicle, in order to assure proper shifting.
^ While driving the vehicle, inspect for loss of power, misfire, or other engine-related driving conditions.

Test Description
2. This step tests for low fluid level, which can cause delayed shifts.
3. This step compares the indicated range signal from the Range Signal table to the Automatic Transmission Fluid Pressure (TFP) manual valve position switch selected gear range.
5. This step tests for low line pressure, which can cause delayed and long shifts.