Circuit Description
The powertrain control module (PCM) detects engine misfire by detecting variations
in crankshaft deceleration between firing strokes. For accurate detection of engine
misfire, the PCM must distinguish between crankshaft deceleration caused by an actual
misfire and deceleration caused by rough road conditions. The Antilock
Brake System (ABS) can detect if the vehicle is on a rough road based
on the wheel acceleration and deceleration data supplied by
the wheel speed sensors. The ABS electronic brake control module (EBCM) transmits
rough road information to the body control module (BCM). The BCM acts as a bus and
sends this information via a UART serial data circuit to the powertrain interface
module (PIM). The PIM converts the UART serial data to Class II serial data
for sharing with the PCM. The PCM can then take the rough road into
account when calculating a misfire. Even if the ABS is malfunctioning
and cannot detect rough roads, the misfire diagnostic
will continue to run. However, if a misfire DTC sets, DTC P1380
also sets indicating that rough road data was not available
during the misfire calculation due to an ABS system malfunction.
DTC Descriptors
This diagnostic procedure supports the following DTC.
DTC P1380 Misfire Detected - Rough Road Data Not Available
Conditions for Running the DTC
• | Engine load is less than 87 percent. |
• | Engine speed is less than 5,000 RPM. |
• | Vehicle speed is greater than 16 km/h (10 mph). |
• | An engine misfire is detected and DTC P0300 is active. |
• | DTC P1380 runs continuously when the above conditions are met. |
Conditions for Setting the DTC
An ABS system malfunction exists, preventing the PCM from receiving the rough
road detection data.
Action Taken When the DTC Sets
• | The control module stores the DTC information into memory when
the diagnostic runs and fails. |
• | The malfunction indicator lamp (MIL) will not illuminate. |
• | The control module records the operating conditions at the time
the diagnostic fails. The control module stores this information in the Failure
Records. |
• | The driver information center, if equipped, may display a message. |
Conditions for Clearing the DTC
• | A current DTC Last Test Failed clears when the diagnostic runs
and passes. |
• | A history DTC clears after 40 consecutive warm-up cycles,
if no failures are reported by this or any other non-emission related diagnostic. |
• | Clear the DTC with a scan tool. |
Diagnostic Aids
For an intermittent condition, refer to
Intermittent Conditions
.
Test Description
The number below refers to the step number on the diagnostic table.
-
Service the ABS system before you diagnose for
a misfire, because an actual engine misfire may or may not exist. The following
examples illustrate how this DTC can be set with or without
an actual engine misfire:
• | There was an actual engine misfire during an ABS system malfunction. |
• | The vehicle operator drove on a rough road, the ABS system could not
detect this due to a malfunction, and the PCM interpreted the variations
in crankshaft speed caused by the rough road as a misfire. |