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Home >> Chevrolet >> 2001 >> Venture Base, Van Passenger >> Repair and Diagnosis >> External Pages >> Different car >> Section 71 (Engine Controls Self-Diagnostics - 2.2L CNG) >> Diagnostic Tests >> DTC P1203: Actual Gas Flow Signal Circuit Frequency High >> Diagnostic Procedures

Diagnostic Procedures

WARNING: This page is about a different car, the 2002 Chevrolet Cavalier. However, it is still accessible from the selected car via links, so may be relevant.
  1. Perform diagnostic system check - engine controls. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS  under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
  2. Using scan tool, capture AF ECM DTC information. Clear AF ECM DTCs. Start engine and view captured data freeze frame records on scan tool for this DTC. Operate the vehicle, within the Conditions for Setting this DTC and the parameters observed when the DTC set, until the scan tool indicates the diagnostic Ran. See CONDITIONS FOR SETTING DTC  . Does the scan tool indicate the diagnostic Passed? If yes, go to next step. If no, go to step  4 .
  3. The fault is not present. See DIAGNOSTIC AIDS  . Are any DTCs stored that have not been diagnosed? If yes, go to DIAGNOSTIC TROUBLE CODE DEFINITIONS  . If no, refer to INTERMITTENT CONDITIONS  under SELF-DIAGNOSTIC SYSTEM.
  4. Turn ignition off. Disconnect the Gas Mass Sensor/Mixture Control Valve (GMS/MCV) connector. Connect the J-39200 Digital Multimeter (DMM) test leads between the GMS/MCV ignition circuit terminal and a known-good ground. Turn ignition on, with engine off. Measure the voltage on the Ignition circuit. Is the voltage within 11-13 volts? If yes, go to next step. If no, go to step  9 .
  5. Connect the J-34142-B 12-Volt Unpowered Test Light between battery positive and the two GMS/MCV ground circuit terminals one at a time. Does the test light illuminate brightly when connected to each ground circuit terminal? If yes, go to next step. If no, go to step  10 .
  6. High frequency signal may be induced on actual gas flow signal circuit by sources other than GMS/MCV sensor. Check for actual gas flow signal circuit routed near secondary ignition components or high current components (motors, relays, etc.). Also check for high power transceivers operating in or near vehicle. Route wiring harness correctly or remove source of high frequency as necessary. Was an induced high frequency source found and corrected? If yes, go to step  12 . If no, go to next step.
  7. Perform fuel system diagnosis. See FUEL SYSTEM DIAGNOSIS under FUEL SYSTEMS (CAVALIER CNG) in SYSTEM & COMPONENT TESTING - CARS - EXCEPT METRO & PRIZM article. Was a CNG fuel system problem found and repaired? If yes, go to step  12 . If no, go to next step.
  8. Replace GMS/MCV. After repairs, go to step  12 .
  9. Turn ignition off and wait 30 seconds. Observe the Fuel Indicator Light (FIL), located in fuel gauge select switch, as you turn ignition on, with engine off. Did the FIL illuminate for a 2 second bulb check or stay ON? If yes, go to step  11 . If no, see IGNITION RELAY DIAGNOSIS (CAVALIER - CNG) under IGNITION SYSTEM in SYSTEM & COMPONENT TESTING - CARS - EXCEPT METRO & PRIZM article.
  10. Repair the GMS/MCV ground circuit with high or infinite/open resistance. After repairs, go to step  12 .
  11. Repair the open ignition circuit between the GMS/MCV connector and the ignition circuit splice. After repairs, go to next step.
  12. Clear the AF ECM DTC Information using the scan tool. Start engine. View the captured data Freeze Frame records for this DTC. Observe the data parameters that give an indication of how the vehicle was being operated when this DTC set. Operate the vehicle, within the Conditions for Setting this DTC and the parameters observed when the DTC set, until the scan tool indicates the diagnostic Ran. See CONDITIONS FOR SETTING DTC  . Does the scan tool indicate the diagnostic Passed? If yes, system is okay. If no, go to step  2 .
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