Engine Controls - Self-Diagnostics - 6.0L Bi-Fuel & Cng: Overview GMC Sierra 1500 HD

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 power may be because of a scan tool or vehicle malfunction. 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-159297-S15239216512003112400000) . 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. 4 The AF lock-off relay also supplies voltage to the Low Pressure Lock-Off (LPL) solenoid. An open circuit between the AF lock-off relay and the splice will cause P2665 to also set.
3. 5 This step verifies that the control module is providing ground to the HPL relay.
4. 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. The FICM monitors the FTT sensor voltage and communicates the data to the PCM by a dedicated pulse width modulated (PWM) 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 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 determines if the Low Pressure Lock-Off (LPL) solenoid is functioning.
3. 5 This step tests the low reference circuit of the FRP sensor.
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 tests the signal circuit of the FRP sensor.
6. 9 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 Fuel Rail Pressure (FRP) sensor is the cause of the condition.
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 Powertrain Control Module (PCM) supplies about 5 volts on the FRP sensor reference voltage circuit. The PCM 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 PCM uses the FRP sensor information in order to adjust fuel trim. 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. The AF fuel mode relay must be removed in order to prevent a fuel system switch-over.
4. 9 This step tests the injector control circuit between the AF injector relay and the PCM. The test light should blink while the engine is cranking.
5. 13 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.
6. 14 This step tests the injector control circuit between the gasoline fuel injector and the AF injector relay. The test light should blink while the engine is running.
7. 16 This step tests the ignition voltage circuit to the AF injector relay. If the relay does not switch during gasoline operation, DTC P0200 will set.
8. 17 This step tests the ground circuit to the AF injector relay. If the relay does not switch during gasoline operation, DTC P0200 will set.

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

1. 3 If DTC P0200 also sets, diagnose P0200 first. A PWM circuit condition between the AF injector relay and the PCM will cause DTCs P0200 and P1020 to set.
2. 5 This step determines if the condition is causing an engine misfire. The AF fuel mode relay must be removed in order to prevent a fuel system switch-over.
3. 6 This step tests the ignition feed circuit to the AF fuel mode relay. An open ignition feed circuit to the relay will set this DTC.
4. 7 This step tests the AF enable circuit to the FICM. An open AF enable circuit between the splice and FICM will set this DTC without an engine misfire.
5. 9 This step verifies that the FICM is receiving the PWM input signal from the PCM. The test light should blink while the engine is cranking.

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

1. 2 The engine must crank or run on CNG in order for this DTC to test.
2. 4 This step verifies that the FICM is able to control the fuel injector. Bi-Fuel (KL6) equipped vehicles must be operating on CNG prior to pulsing the CNG fuel injector.
3. 5 This step tests if a ground is constantly being applied to the fuel injector.
4. 10 A short to ground of the CNG injector battery positive circuit will open the inline fuse and cause an entire cylinder bank to set DTC's. Test the CNG injector battery positive circuits, bank injector monitor circuit and the FICM for a shorted condition whenever the inline fuse has opened.

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. 5 This step verifies that the PCM 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. 5 This step verifies that the PCM is supplying the correct output voltage. The open circuit voltage should be 5.0 volts.

The CNG Fuel Tank Pressure (FTP) sensor is a pressure transducer. The Fuel Injector Control Module (FICM) supplies about 5 volts on the FTP sensor reference voltage circuit. The FICM also supplies a signal circuit and a low reference 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 FICM communicates the FTP data to the Powertrain Control Module (PCM) by a Pulse Width Modulated (PWM) circuit. The PCM uses the FTP sensor and the Fuel Tank Temperature (FTT) sensor in order to determine 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 CNG Fuel Tank Pressure (FTP) sensor is a pressure transducer. The Fuel Injector Control Module (FICM) supplies about 5 volts on the FTP sensor reference voltage circuit. The FICM also supplies a signal circuit and a low reference 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 FICM communicates the FTP data to the Powertrain Control Module (PCM) by a Pulse Width Modulated (PWM) circuit. The PCM uses the FTP sensor and the Fuel Tank Temperature (FTT) sensor in order to determine 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. 5 This step determines if the PCM is receiving 12 volts from the AF fuel mode relay.

1. 2 This step determines if an AF lock-off relay condition is the cause of the concern. A faulty relay will cause DTC P0005 to also set.
2. 3 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.
3. 5 This step tests the ignition voltage circuit to the LPL solenoid.
4. 6 This step verifies that the control module is providing ground to the LPL solenoid.
5. 7 This step tests if a ground is constantly being applied to the LPL solenoid.