Circuit Description
The PCM supplies a voltage to the engine speed output circuit. The PCM
creates the engine speed output signal by rapidly grounding this circuit via
an internal switch called a driver.
The driver supplies the ground for the component being controlled. Each
driver has a fault line which the PCM monitors. When the PCM commands a component
ON, the voltage of the control circuit should be low (near
0 volts). When the PCM commands the control circuit
to a component OFF, the voltage potential of the circuit should
be high (near battery voltage). If the fault detection circuit
senses a voltage other than what is expected, the fault line
status changes causing the DTC to set.
Conditions for Running the DTC
| • | The engine speed is greater than 400 RPM. |
| • | The ignition voltage is between 6.0 volts and 18.0 volts. |
Conditions for Setting the DTC
| • | The PCM detects that the commanded state of the driver and the
actual state of the control circuit do not match. |
| • | All conditions present for a minimum of 2.0 seconds. |
Action Taken When the DTC Sets
| • | The PCM illuminates the Malfunction Indicator Lamp (MIL) on the
second consecutive drive trip that the diagnostic runs and fails. |
| • | The PCM records the operating conditions at the time the diagnostic
fails. The first time the diagnostic fails, the Failure Records will store
this information. If the diagnostic reports a failure on the second consecutive
drive trip, the Freeze Frame records the operating conditions at the
time of failure and updates the Failure Records. |
Conditions for Clearing the MIL/DTC
| • | The PCM will turn the MIL off after three consecutive trips without
a fault condition. |
| • | A History DTC clears after forty consecutive warm-up cycles,
if this or any other emission related diagnostic does not report any failures. |
Diagnostic Aids
Important: Remove any debris from the PCM connector surfaces before servicing the
PCM. Inspect the PCM connector gaskets when diagnosing/replacing the
PCM. Ensure that the gaskets are installed correctly. The gaskets
prevent water intrusion into the PCM.
Using Freeze Frame and/or Failure Records data may aid in locating an
intermittent condition. If you cannot duplicate the DTC, the information included
in the Freeze Frame and/or Failure Records data can aid in
determining how many miles since the DTC set. The Fail Counter
and Pass Counter can also aid determining how many ignition
cycles the diagnostic reported a pass and/or a fail. Operate
the vehicle within the same freeze frame conditions (RPM,
load, vehicle speed, temperature etc.) that you observed. This
will isolate when the DTC failed.
