Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSCHEVROLET1999ASTRO VAN 2WD V6-4.3L VIN WREPAIR AND DIAGNOSISPOWERTRAIN MANAGEMENTCOMPUTERS AND CONTROL SYSTEMSENGINE CONTROL MODULEDESCRIPTION AND OPERATIONMISFIRE MONITOR DIAGNOSTIC TESTS
1999 Chevrolet Astro Van 2WD V6-4.3L VIN W
Misfire Monitor Diagnostic Tests
1999 Chevrolet Astro Van 2WD V6-4.3L VIN WSECTION Misfire Monitor Diagnostic Tests
When the engine is running and a cylinder misfires the crankshaft slows down momentarily. The control module has the ability to detect this change in speed by monitoring the input signals from the following sensors:
^ The Crankshaft Position (CKP) sensor
^ The Camshaft Position (CMP) sensor.
When the control module is running the misfire on-board diagnostic tests and a misfire is detected the misfire counter stores (accumulates) the position and the number of misfires. Two counters (accumulators) are assigned to each of the cylinders. The counters are as follows:
^ The Current Misfire Counters. The current misfire counters store the number misfires that have occurred in the last 200 engine cycles. When the control module detects an unacceptable amount of misfires stored in a current misfire counter, the misfire on-board diagnostic test fails and a misfire DTC will set.
^ The History Misfire Counters. When a misfire DTC is set, the history misfire counters store the total number of misfires that have occurred every 200 engine cycles.
^ The Crankshaft Position (CKP) sensor
^ The Camshaft Position (CMP) sensor.
When the control module is running the misfire on-board diagnostic tests and a misfire is detected the misfire counter stores (accumulates) the position and the number of misfires. Two counters (accumulators) are assigned to each of the cylinders. The counters are as follows:
^ The Current Misfire Counters. The current misfire counters store the number misfires that have occurred in the last 200 engine cycles. When the control module detects an unacceptable amount of misfires stored in a current misfire counter, the misfire on-board diagnostic test fails and a misfire DTC will set.
^ The History Misfire Counters. When a misfire DTC is set, the history misfire counters store the total number of misfires that have occurred every 200 engine cycles.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.