P047

UART Circuit:

DESCRIPTION
The Powertrain Control Module (PCM) and Instrument Panel Cluster (IPC) share information through the Universal Asynchronous Receiver Transmitter (UART) data link. The IPC is the "Master" of the link and data is only transmitted at the IPC's request. Data is sent in eight-character "Words" at the rate of 8192 characters per second.

The data from the PCM to the IPC contains engine operating information. The PCM-IPC data includes Engine Coolant Temperature Sensor, RPM and Injector Pulse width values so the IPC can control cooling fans, display rpm and calculate MPG for display at the driver information center. The IPC sends the PCM air conditioning status to be used for idle speed control and ambient (outside) temperature for use in Torque Converter Clutch (TCC) apply and release decisions.

Code P047 is logged in the PCM in the event of a UART fault. If the fault is a current failure, the PCM will not be able to communicate with the IPC and Code 1034 will be displayed as current. (Code P047 is current in the PCM but can't be sent to the IPC because of the UART fault.) If the UART fault is corrected, both Code P047 and Code 1034 will be displayed as history codes.

DIAGNOSTIC CIRCUIT CHECK
^ Code PO47 can only be displayed as an intermittent. If the fault is present, code I034 will be current and PCM data cannot be displayed.

^ The following failures will result in a code PO47 stored as history:

- Both 800 circuits from the PCM to IPC open. Symptom will be:

a. "System Fault" message on Driver Information Center (DIC)
b. "Service Engine Soon" and "Check Info Center" Malfunction Indicator Lamp (MIL) "ON"
c. Entering diagnostics "No PCM Data" displayed on DIC
d. When fault is repaired, PO47 and I034 will be history

- CKT 800 shorted to ground at any point. Symptoms will be:

a. "System Fault" message on DIC
b. "Service Engine Soon" MIL "ON"
c. Instrument panel gauges will flash
d. Climate control goes blank
e. Engine cooling fans go high
f. Diagnostics cannot be entered - DIC stays at "System Fault"
g. When fault is repaired, will show PO47, I033, I034, and I037 history

AFTER REPAIRS
When all diagnosis and repairs are completed, clear codes and verify operation.

TEST CONDITIONS
1. Code P012 not set.
2. Engine speed 500 RPM or greater RPM for 20 seconds.

FAILURE CONDITIONS
PCM receives invalid data from IPC for 5 seconds.

ACTION TAKEN
1. PCM turns "ON" the "Service Engine Soon" MIL.
2. PCM sets all incoming data to zero.
3. PCM boosts idle to compensate for possible A/C clutch engagement.
4. Cooling fan control will be based on engine coolant temperature only.