Engine Controls Self-Diagnostics - 6.0L Bi-Fuel & Cng: Overview GMC Savana H2500

Description

The Diagnostic System Check - Alternative Fuels - Engine Controls is an organized approach to identifying a condition that is created by a malfunction in the engine control system. The diagnostic system check must be the starting point for any driveability concern. The diagnostic system check directs the service technician to the next logical step in order to diagnose the concern. Understanding and correctly using the diagnostic test procedure reduces diagnostic time and prevents the replacement of good parts.

Test Description

The numbers below refer to the step numbers in the diagnostic procedure.

1. 1 Lack of communication may be because of a partial or a total malfunction of the class 2 serial data circuit. The specified procedure determines the particular condition.
2. 2 Lack of communication may be because of a partial or a total malfunction of the class 2 serial data circuit. The specified procedure determines the particular condition.
3. 3 This step determines if the vehicle will start.
4. 5 This step stores the Powertrain Control Module (PCM) Diagnostic Trouble Code (DTC) information into the scan tools memory. After you complete the diagnostic procedure, review the captured information in order to catch the next DTC if the control module stores multiple DTCs. Review the Freeze Frame/Failure Records data. Use this information in order to determine how frequently and how recently the DTC set. This information may help diagnose an intermittent condition. Information about the operating conditions at the time that the DTC set may also help diagnose an intermittent condition. Capturing the stored information saves the data that the PCM loses during the following conditions: When a diagnostic procedures instructs you to clear the DTCs. When a diagnostic procedure instructs you to disconnect the PCM connectors. When a diagnostic procedure instructs you to replace the PCM.
5. 6 The presence of DTCs which begin with "U", indicate that some other module is not communicating. Following the specified procedure will gather all the available information before you perform the tests.
6. 9 If there are other modules with DTCs set, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-159156-S06111585432003111300000) . The DTC list directs you to the appropriate diagnostic procedure. If the control module stores multiple powertrain DTCs, diagnose the DTCs in the following order: Component level DTCs, such as sensor DTCs, solenoid DTCs, and relay DTCs. Diagnose the multiple DTCs within this category in numerical order. Begin with the lowest numbered DTC, unless the diagnostic test directs you otherwise. System level DTCs, for example, misfire DTCs, fuel trim DTCs, and catalyst DTCs.
7. 11 This step determines if the vehicle will operate on the gasoline fuel system.
8. 13 This step is for areas that have inspection and maintenance testing procedures for emissions testing. Use this step if the testing facility found one or more I/M system statuses that did not set.

The numbers below refer to the step numbers in the diagnostic procedure.

1. 2 This step tests if the concern is active. You should hear a clicking sound when the High Pressure Lock-Off (HPL) relay is commanded ON and OFF. Repeat the commands as necessary.
2. 5 This step verifies that the control module is providing ground to the HPL relay.
3. 6 This step tests if a ground is constantly being applied to the HPL relay.

The numbers below refer to the step numbers in the diagnostic procedure.

1. 2 This step determines if the condition is active. The Powertrain Control Module (PCM) grounds the Alternative Fuel (AF) enable circuit when operating on CNG.
2. 4 This step tests for a short to ground on the AF enable circuit. The test light should not illuminate with the ignition off.

The numbers below refer to the step numbers in the diagnostic procedure.

1. 5 If conditions were not corrected, see «FUEL SYSTEM DIAGNOSIS»(ref-152801-S36073921212003022600000) under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 6.0L CHEVY EXPRESS, SAVANA, SIERRA & SILVERADO - BI-FUEL & CNG article.
2. 6 If conditions were not corrected, a worn cam, worn intake or exhaust valves, or other engine mechanical failure may be the problem.

The numbers below refer to the step numbers in the diagnostic procedure.

1. 5 If the cause of the DTC is not found and corrected, see «FUEL SYSTEM DIAGNOSIS»(ref-152801-S36073921212003022600000) under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 6.0L CHEVY EXPRESS, SAVANA, SIERRA & SILVERADO - BI-FUEL & CNG article.
2. 6 On KL6 equipped vehicles, an EVAP canister that is saturated will cause a rich condition. If the condition is not found, a worn cam, worn intake or exhaust valves, or other engine mechanical failure may be the cause of the DTC.

The Fuel Tank Temperature (FTT) sensor is a variable resistor that measures the temperature of the fuel in the CNG fuel tank. The PCM supplies 5 volts to the FTT signal circuit. This DTC sets when the FTT signal voltage is above the normal operating range of the sensor.

The numbers below refer to the step numbers in the diagnostic procedure.

1. 4 Tests for the proper operation of the circuit in the low voltage range. If the fuse in the jumper opens when you perform this test, the signal circuit is shorted to voltage.
2. 8 This step tests the signal circuit of the FTT sensor for a short to another 5-volt reference circuit.

The Fuel Rail Temperature (FRT) sensor is a variable resistor that measures the temperature of the fuel in the CNG fuel rail. The Fuel Injector Control Module (FICM) supplies 5 volts to the FRT signal circuit and supplies a ground to the low reference circuit. The FICM monitors the FRT sensor voltage and communicates the data to the PCM by a dedicated Pulse Width Modulated (PWM) circuit. This DTC sets when the FRT signal voltage is below the normal operating range of the sensor.

The numbers below refer to the step numbers in the diagnostic procedure.

1. 2 This step determines if the condition exists.
2. 3 This step determines if an open low reference circuit is the cause of the condition. If DTC P0192 is also set, an open low reference circuit may be the cause. The Fuel Rail Temperature (FRT) sensor, and the Fuel Rail Pressure (FRP) sensor share a low reference circuit.

The Fuel Rail Temperature (FRT) sensor is a variable resistor that measures the temperature of the fuel in the CNG fuel rail. The Fuel Injector Control Module (FICM) supplies 5 volts to the FRT signal circuit and supplies a ground to the low reference circuit. The FICM monitors the FRT sensor voltage and communicates the data to the PCM by a dedicated Pulse Width Modulated (PWM) circuit. This DTC sets when the FRT signal voltage is above the normal operating range of the sensor.

The number below refer to the step number in the diagnostic procedure.

1. 4 Tests for the proper operation of the circuit in the low voltage range. If the fuse in the jumper opens when you perform this test, the signal circuit is shorted to voltage.

The numbers below refer to the step numbers in the diagnostic procedure.

1. 2 This step determines if the condition is present.
2. 4 This step tests the FRP sensor signal circuit and the low reference circuit. The scan tool should display zero volts when the circuits are jumpered together.
3. 5 This step determines if the signal circuit of the FRP sensor is the cause of the condition. The scan tool should display zero volts when the signal circuit is jumpered to a good ground.
4. 6 This step determines if the 5-volt reference circuit is the cause of the condition. The DVOM should display 5.0 volts across the test light.
5. 7 This step verifies that a mechanical fuel system condition is not the cause of the concern. A fuel pressure regulator condition may cause this DTC to set.

The Fuel Rail Pressure (FRP) sensor is a pressure sensor. The Fuel Injector Control Module (FICM) supplies about 5 volts on the FRP sensor reference voltage circuit. The FICM also supplies a ground circuit and a signal circuit to the FRP sensor. When the fuel rail pressure is normal, the FRP signal voltage rises to near 2.5 volts. If the fuel rail pressure increases, the FRP signal voltage increases. The FICM monitors the FRP sensor voltage and communicates the data to the PCM by a dedicated Pulse Width Modulated (PWM) circuit. This DTC sets when the FRP sensor signal voltage is below the normal operating range of the sensor.

The numbers below refer to the step numbers in the diagnostic procedure.

1. 2 This step determines if the condition is present.
2. 4 This step determines if the signal circuit of the Fuel Rail Pressure (FRP) sensor is the cause of the condition. The FRP sensor voltage will increase from zero volts to above one volt, with the sensor disconnected.
3. 5 This step determines if the 5-volt reference circuit is the cause of the condition.

The Fuel Rail Pressure (FRP) sensor is a pressure sensor. The Fuel Injector Control Module (FICM) supplies about 5 volts on the FRP sensor reference voltage circuit. The FICM also supplies a ground circuit and a signal circuit to the FRP sensor. When the fuel rail pressure is normal, the FRP signal voltage rises to near 2.5 volts. If the fuel rail pressure increases, the FRP signal voltage increases. The FICM monitors the FRP sensor voltage and communicates the data to the PCM by a dedicated Pulse Width Modulated (PWM) circuit. This DTC sets when the FRP sensor signal voltage is more than the normal operating range of the sensor.

The numbers below refer to the step numbers in the diagnostic procedure.

1. 2 This step determines if the condition is present.
2. 4 This step determines if an open sensor ground circuit condition the cause of the condition. The Fuel Rail Pressure (FRP) sensor and the Fuel Rail Temperature (FRT) sensor share a common ground. An open circuit between the splice and the FICM will cause both signal circuits to indicate a high voltage.
3. 5 This step determines if an open or shorted signal circuit is the cause of the condition.
4. 6 This step determines if a shorted 5-volt reference circuit is the cause of the condition.
5. 7 This step determines if an open sensor ground circuit between the harness connector of the FRP sensor and the splice is the cause of the condition.

The numbers below refer to the step numbers in the diagnostic procedure.

1. 2 This step verifies that a condition exists.
2. 4 The step determines if the condition occurs during gasoline operation. If the vehicle misfires while on gasoline, then the condition is between the Fuel Injection Control Module (FICM) and the gasoline fuel injector.
3. 6 This step tests the control circuit between the PCM and the FICM. The test light should blink while the engine is cranking.
4. 10 This step verifies that an ignition voltage is supplied to the gasoline fuel injector. If the ignition voltage circuit is open DTC P0200 will set while operating on gasoline.
5. 11 This step tests the control circuit between the FICM and the gasoline fuel injector. A switch to gasoline is necessary in order to pulse the gasoline fuel injectors. The test light should blink while the engine is operating.

The numbers below refer to the step numbers in the diagnostic procedure.

1. 5 This step determines if the engine is misfiring while operating on the gasoline fuel system.
2. 7 If the Misfire Current Counters are incrementing, but the engine is NOT misfiring, this indicates a mechanical condition. For example, an accessory drive belt could cause this condition.
3. 8 This step verifies that the Crankshaft Variation Learn Procedure is performed. A crankshaft variation that is not learned may cause the misfire counters to increment.
4. 10 The spark should be consistent when you test the spark at the spark plug wires. The presence of few sparks then nothing indicates no spark.
5. 14 A misfiring cylinder may cause more than one misfire counter to increment. Diagnose the fuel injector circuit of the cylinder that displays the highest level of misfire.
6. 20 This step verifies that the catalytic convertors are operating correctly.

The number below refers to the step number on the diagnostic table.

1. 2 This step verifies that the condition is active.
2. 3 This step verifies that the ignition voltage circuit to the FICM is OK. If the ignition voltage circuit is open, DTCs P1207, P1208, and P1209 may also be set.

The numbers below refer to the step numbers in the diagnostic procedure.

1. 5 This step verifies that the Fuel Injector Control Module (FICM) is able to control the fuel injector.
2. 6 This step tests if a ground is constantly being applied to the fuel injector.

The numbers below refer to the step numbers in the diagnostic procedure.

1. 4 This step determines if a CNG related DTC is set.
2. 5 This step determines if the condition is present.
3. 7 This step determines if the CNG fuel system is the cause of the concern.

The numbers below refer to the step numbers in the diagnostic procedure.

1. 2 This step determines if the condition is present.
2. 3 If any of the listed DTCs are set, diagnose those DTCs first.
3. 5 This step determines if a Fuel Rail Pressure (FRP) sensor circuit may be the cause of the condition. If a FRP sensor circuit condition exists, the FICM will output zero percent PWM to the PCM. With the FRP sensor disconnected, the fuel rail pressure should slowly rise.
4. 6 This step verifies that the FICM is supplying 5 volts on the FRP sensor reference circuit. An open, or a short to ground, on the 5 volt reference circuit may set this DTC.
5. 7 This step verifies that the FICM is supplying a low reference circuit. An open on the FRP sensor low reference circuit may set this DTC.
6. 8 This step determines if the signal circuit of the FRP sensor is shorted to a voltage. A short to a voltage on the signal circuit of the FRP sensor may set this DTC.
7. 9 This step determines if the signal circuit of the FRP sensor is shorted to ground. A short to ground on the signal circuit of the FRP sensor may set this DTC. The DVOM will display OL If the signal circuit is not grounded.
8. 10 This step verifies that the FICM is supplying the correct output voltage on the FRP output PWM circuit. The open circuit voltage should be 5.0 volts.

The numbers below refer to the step numbers in the diagnostic procedure.

1. 2 This step determines if the condition is present.
2. 3 If any of the listed DTCs are set, diagnose those DTCs first.
3. 5 This step tests the signal circuit of the Fuel Rail Temperature (FRT) sensor. The DVOM should display 5 volts.
4. 7 This step tests the low reference circuit of the FRT sensor. An open FRT sensor low reference circuit may cause this DTC to set.
5. 8 This step determines if the FICM, PCM, and the rail temperature output PWM circuit are OK. If the temperature parameter changes when the FRT signal circuit is grounded, the FICM, PCM, and wiring are OK. Repeat the procedure as necessary in order to verify correct operation of the FICM, PCM, and the rail temperature output PWM circuit.
6. 9 This step verifies that the FICM is supplying the correct output voltage. The open circuit voltage should be 5.0 volts.

The numbers below refer to the step numbers in the diagnostic procedure.

1. 2 This step determines if the condition is present.
2. 3 If any of the listed DTCs are set, diagnose those DTCs first.
3. 5 This step verifies that the Fuel Injection Control Module (FICM) is supplying the correct output voltage. The open circuit voltage should be 5.0 volts.

The Fuel Tank Pressure (FTP) sensor is a pressure transducer. The Powertrain Control Module (PCM) supplies about 5 volts on the FTP sensor reference voltage circuit. The PCM also supplies a signal circuit to the FTP sensor. When fuel level/tank pressure is full the FTP signal voltage rises to 4.1 volts. As fuel level/tank pressure decreases to empty, the FTP signal voltage drops to around 0.5 volts. The PCM monitors the FTP signal circuit voltage and the Fuel Tank Temperature (FTT) sensor and determines the amount of fuel within the fuel tank. This DTC sets when the FTP sensor signal voltage is below the normal operating range of the sensor.

The numbers below refer to the step numbers in the diagnostic procedure.

1. 2 This step determines if the failure condition is present.
2. 4 This step determines if the Fuel Tank Pressure (FTP) sensor is the cause of the failure condition.
3. 5 This step determines if the 5-volt reference circuit is the cause of the failure condition.

The Fuel Tank Pressure (FTP) sensor is a pressure transducer. The Powertrain Control Module (PCM) supplies about 5 volts on the FTP sensor reference voltage circuit. The PCM also supplies a signal circuit to the FTP sensor. When fuel level/tank pressure is full the FTP signal voltage rises to 4.1 volts. As fuel level/tank pressure decreases to empty, the FTP signal voltage drops to around 0.5 volts. The PCM monitors the FTP signal circuit voltage and the Fuel Tank Temperature (FTT) sensor and determines the amount of fuel within the fuel tank. This DTC sets when the FTP sensor signal voltage is greater than the normal operating range of the sensor.

The numbers below refer to the step numbers in the diagnostic procedure.

1. 2 This step determines if the failure condition is present.
2. 4 This step determines if an open sensor ground circuit condition is present. The Fuel Tank Pressure (FTP) and Fuel Tank Temperature (FTT) sensors share a common ground. An open circuit between the splice and the ground terminal will cause both signal circuits to indicate high voltage.
3. 5 This step determines if an open or shorted signal circuit is the cause of the failure condition.
4. 6 This step determines if a shorted 5-volt reference circuit is the cause of the failure condition.
5. 7 This step determines if an open sensor ground circuit between the FTP connector and the circuit splice is the cause of the failure condition.

The numbers below refer to the step numbers in the diagnostic procedure.

1. 2 This step tests if the concern is active.
2. 4 This step tests if a ground is constantly being applied to the AFO enable circuit. With the FICM disconnected, the PCM will command gasoline operation. The AFO enable circuit should not illuminate the test light.
3. 5 This step verifies that the PCM is providing ground to the AFO enable circuit.

1. 2 This step tests if the concern is active. You should hear a clicking sound when the Low Pressure Lock-Off (LPL) relay is commanded on and off. Repeat the commands as necessary.
2. 5 This step verifies that the control module is providing ground to the LPL relay.
3. 6 This step tests if a ground is constantly being applied to the LPL relay.

The numbers below refer to the step numbers in the diagnostic procedure.

1. 2 This step tests if the concern is active. The Fuel Indicator Light (FIL) should turn on and off with the scan tool commands. Repeat the commands as necessary.
2. 5 This step verifies that the control module is providing ground to the FIL.
3. 6 This step tests if a ground is constantly being applied to the FIL.