K 3500 Truck 4WD V8-5.7L VIN R (1998)
Prior to repairing a vehicle, use the status information in order to evaluate the state of the diagnostic test and to help identify an intermittent problem.
The technician can conclude that although the MIL is illuminated, the fault condition that caused the code to set is not present. An intermittent
condition must be the cause.
Malfunction Indicator Lamp (MIL)
(MIL)
The (MIL) Malfunction Indicator Lamp is on the instrument panel. The MIL has the following functions:
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The MIL informs the driver that a fault that affects the emission levels of the vehicle has occurred. The owner should take the vehicle in for
service as soon as possible.
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As a bulb and system check, the MIL (Malfunction Indicator Lamp) comes ON with the key ON and the engine not running. When the engine
is started, the MIL turns OFF if no DTCs are set.
When the MIL remains ON while the engine is running, or when a malfunction is suspected due to a driveability or emissions problem, perform an
On-Board Diagnostic (OBD) System Check. See: Testing and Inspection
The procedures for these checks are given in engine controls. These checks expose faults which the technician may not detect if other diagnostics are
performed first.
INTERMITTENT MALFUNCTION INDICATOR LAMP
In the case of an intermittent fault, the MIL (Malfunction Indicator Lamp) may illuminate and then after 3 trips turn OFF. However, the corresponding
diagnostic trouble code will store in the memory. When unexpected diagnostic trouble codes appear, check for an intermittent malfunction.
MIL Requests and History Codes
MIL REQUESTS AND HISTORY CODES
The Diagnostic Executive must acknowledge when all the emissions related diagnostic tests have reported a pass or fail condition since the last
ignition cycle. Each diagnostic test is separated into 4 types:
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Type A - Is emissions related, and turns ON the MIL the first time the diagnostic executive reports a fault.
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Type B - Is emissions related, and turns ON the MIL if the fault is active for 2 consecutive driving cycles.
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Type C - Is non-emissions related, and does not turn ON the MIL but will turn on the service light.
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Type D - is non -emission related and does not turn ON the MIL or the service light.
DIAGNOSTIC EXECUTIVE / TYPE A, B, & C DIAGNOSTIC TESTS
When a type A diagnostic test reports a failure, the Diagnostic Executive immediately' requests to have the MIL turn ON for that diagnostic test. When
a type B diagnostic test reports a failure during 2 consecutive trips, the Diagnostic Executive turns on the MIL for that diagnostic test. The Diagnostic
Executive has the option of turning the MIL OFF when the diagnostic test which caused the MIL to illuminate the passes for 3 consecutive trips. In the
case of misfire or fuel trim malfunctions, there are additional requirements as follows:
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The load conditions must be within 10% of the vehicle load present when the diagnostic executive reported the failure.
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The engine speed conditions must be within 375 RPM of the engine speed present when the diagnostic executive reported the failure.
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The engine coolant temperature must have been in the same range present when the diagnostic executive reported the failure.
When the Diagnostic Executive requests the service light to be turned ON or a type C diagnostic fault is reported, a history DTC is also recorded for
the diagnostic test. The provision for clearing a history DTC for any diagnostic tests requires 40 subsequent warm-up cycles during which no
diagnostic tests have reported a fail, a battery disconnect, or a scan tool clear info command.
SPECIAL CASES OF TYPE A DIAGNOSTIC TESTS
Unique to the misfire diagnostic, the Diagnostic Executive has the capability of alerting the driver of potentially damaging levels of misfire. If a
misfire condition exists that could potentially damage the catalytic converter, the Diagnostic Executive will command the MIL to flash at a rate of
once per second during the times that the catalyst damaging misfire condition is present.
SPECIAL CASES OF TYPE B DIAGNOSTIC TESTS
Misfire and fuel trim malfunctions are special cases of type B diagnostics. Each time a fuel trim malfunction is detected, the engine load, the engine
speed, and the engine coolant temperatures are recorded.
When the ignition is turned off, the last reported set of conditions remain stored. During subsequent ignition cycles, the stored conditions are used as a
reference for similar conditions. If a fuel trim malfunction occurs during 2 consecutive trips, the Diagnostic Executive treats the failure as a normal
type B diagnostic. The Diagnostic Executive does not use the stored conditions. However, if a fuel trim malfunction occurs on 2 non-consecutive trips,
the stored conditions are compared with the current conditions. The MIL will then illuminate under the following conditions:
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When the engine load conditions are within 10% of the previous test that failed.
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The engine speed is within 375 RPM of the previous test that failed.
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The engine coolant temperature is in the same range as the previous test that failed.
Storing and Erasing Freeze Frame Data
