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Wiring diagrams Section: Testing & Diagnostics

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Engine Controls Self-Diagnostics - 6.0L - Bi-Fuel & Cng: Other GMC Sierra 2500

Testing & Diagnostics ~1586 words

Code Types

There are 4 types of DTC categories

Type "A" Emissions related. Illuminates MIL the first time DTC sets.
Type "B" Emissions related. Illuminates MIL if fault is active for 2 consecutive driving cycles.
Type "C" Non-emissions related. Does not illuminate MIL, but will illuminate SERVICE light.
Type "D" Non-emissions related. Does not illuminate MIL or SERVICE light.

Freeze Frame/Failure Records

AF ECM stores one freeze frame record for the first failed test that sets a DTC and illuminates MIL. Freeze frame will not be overwritten unless a misfire or fuel trim DTC is set. Failure records are stored when any DTC is set. Some control modules can store up to 5 failure records. Failure records will be stored for all types of codes, whether or not the MIL is illuminated.

Typical data includes

Air/fuel ratio.
Airflow rate.
Fuel trim.
Engine speed.
Engine load.
Engine coolant temperature.
Vehicle speed.
Throttle position angle.
Manifold absolute pressure.
Injector base pulse width.
Loop status.

Monitors

Note. Not all monitors will run while operating in CNG mode. In order to complete all monitors, the vehicle will also need to operate in gasoline mode.

Comprehensive Component Monitor Monitors PCM systems for opens, shorts grounds and out-of-range sensors. Also monitors rationality of sensors. Rationality is whether the sensors value is consistent with the operating conditions of the other sensors.
Misfire Monitor Monitors engine misfire using crankshaft sensor to determine location and severity of misfire. A catalyst damaging misfire will flash the MIL, and a non-catalyst damaging misfire is a normal type "B" code.
Fuel Trim Monitor Monitors short and long term fuel trim for being at maximum lean or rich limit.
Oxygen Sensor Monitor Monitors all oxygen sensors for maximum voltage level, minimum voltage level and lean rich/rich lean switching rate.
Oxygen Sensor Heater Monitor Monitors oxygen sensor heater by watching sensor's time-to-activity after a cold start.
Catalyst Monitor Monitors catalyst efficiency by comparing activity rate of pre-catalyst oxygen sensor and post-catalyst oxygen sensor.
EVAP Monitor Monitors EVAP system for large leaks, small leaks and purge flow.

INTERMITTENT CONDITIONS

Note. Intermittent is a DTC or symptom, with a condition that cannot be duplicated.

Preliminary

Perform the Diagnostic System Check - Engine Controls before starting. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS .

Control Module Power & Grounds, & Component Power & Grounds

Poor power or ground connections can cause widely varying symptoms.

Test all control module power circuits. Many vehicles have multiple circuits supplying power to the control module. Other components in the system may have separate power circuits that may also need to be tested. Inspect connections at the module or component connectors, fuses, and any intermediate connections between the power source and the module or component. A test light or a Digital Multimeter (DMM) may indicate that voltage is present, but neither tests the ability of a circuit to carry sufficient current. Ensure that the circuit can carry the current necessary to operate the component. See WIRING DIAGRAMS article.
Test all control module ground and system ground circuits. The control module may have multiple ground circuits. Other components in the system may have separate grounds that may also need to be tested. Inspect grounds for clean and tight connections at the grounding point. Inspect the connections at the component and in splice packs, where applicable. Ensure that the circuit can carry the current necessary to operate the component. See WIRING DIAGRAMS article.

Temperature Sensitivity

An intermittent condition may occur when a component or connection reaches normal operating temperature. The condition may occur only when the component or connection is cold, or only when the connection is hot.
The following data may help to diagnose this type of intermittent condition: Freeze Frame/Failure Records. Scan tool snapshot. Vehicle data recorder.
If the intermittent is related to heat, review the following data: High ambient temperatures. Underhood or engine generated heat. Circuit generated heat due to a poor connection, or high electrical load. Higher than normal load conditions, such as towing.
If the intermittent is related to cold, review the following data: Low ambient temperatures. In extremely low temperatures, ice may form in a connection or component. Test for water intrusion. The condition only occurs on a cold start. The condition is not present after the vehicle warms up.
Information from the customer may help to determine if the trouble follows a pattern that is temperature related.

Incorrect PCM Programming

There are only a few situations when reprogramming a PCM is appropriate, such as the following: A new service PCM is installed. A PCM from another vehicle is installed. Revised software or calibration files have been released for this vehicle. NOTE: DO NOT reprogram the PCM with the SAME software or calibration files that are already present in the PCM. This is not an effective repair for any type of driveability problem.
Verify that the PCM contains the correct software or calibration. If incorrect programming is found, reprogram the PCM with the most current software or calibration. See «POWERTRAIN CONTROL MODULE REPROGRAMMING»(ref-151060-S08163205432002120600000) under PROGRAMMING.

Duplicating Failure Conditions

If none of the previous tests are successful, attempt to duplicate or capture the failure conditions.
Freeze Frame/Failure Records data, where applicable, contains the conditions that were present when the DTC set. Perform the following procedure: Review and record Freeze Frame/Failure Records data. Clear the DTCs using the scan tool. Turn the key to OFF and wait 15 seconds. Operate the vehicle under the same conditions that were noted in Freeze Frame/Failure Records data, as closely as possible. The vehicle must also be operating within the Conditions for Running the DTC. Monitor DTC Status for the DTC being tested. The scan tool will indicate Ran, when the enabling conditions have been satisfied long enough for the DTC to run. The scan tool will also indicate whether the DTC passed or failed.
An alternate method is to drive the vehicle with the Digital Multimeter (DMM) connected to a suspected circuit. An abnormal reading on the DMM when problem occurs, may help you locate the problem.

Vehicle Data Recorder

The Vehicle Data Recorder (J-42598) is connected to the Data Link Connector (DLC) and sent with the customer. The J-42598 captures data for later retrieval and analysis by the technician. Refer to the vehicle data recorder user instructions for more information.

Disconnect Battery

Note. On many OBD-II systems, PCM will retain memory for an extended period of time with battery disconnected. Memory may be retained for several days.

Disconnecting PCM power or battery ground will clear all PCM memory including DTCs, freeze frame, failure records, adaptive learning and system monitors.

Warm-up Cycles

If fault that caused DTC to set is repaired, PCM will begin to count warm-up cycles. After 40 consecutive warm-up cycles with no further faults, PCM will automatically clear DTC from memory.

ALTERNATIVE FUEL ENGINE CONTROL MODULE

After replacing Alternative Fuel Engine Control Module (AF ECM) or if program needs to be updated (flashed), refer to latest Techline(tm) information on AF ECM reprogramming.

POWERTRAIN CONTROL MODULE REPROGRAMMING

To program PCM or if program needs to be updated, see POWERTRAIN CONTROL MODULE under PROGRAMMING in SELF-DIAGNOSTICS - 4.8L, 5.3L & 6.0L "C" & "K" SERIES TRUCKS article. After reprogramming, perform CRANKSHAFT POSITION SENSOR and THEFT DETERRENT PASSWORD LEARN PROCEDURE .

CRANKSHAFT POSITION SENSOR

Note. To perform CKP variation learn procedure, a switchover to gasoline operation is necessary. Remove CNG fuse (20-amp) located in underhood fuse block to perform switchover.

Note. Battery must be fully charged and in good condition. Scan tool connection at Data Link Connector (DLC) should be clean and tight before starting crankshaft position system variation learn procedure.

To program crankshaft position sensor, see CRANKSHAFT POSITION SENSOR under PROGRAMMING in SELF-DIAGNOSTICS - 4.8L, 5.3L & 6.0L "C" & "K" SERIES TRUCKS article.

THEFT DETERRENT PASSWORD LEARN PROCEDURE

Note. The BODY CONTROL MODULE (BCM) must be programmed with the proper RPO configurations before performing learn procedures. See PROGRAMMING in appropriate BODY CONTROL MODULES article. If replacing the BCM with a GM Service Parts Operations (SPO) replacement part, the module will learn passlock(tm) sensor data code immediately. The existing PCM however, must learn the new fuel continue password when the BCM is replaced. If replacing a PCM with a GM SPO replacement part, after programming, these modules will learn the incoming fuel continue password immediately upon receipt of a password message. Once a password message is received, and a password is learned, a learn procedure must be performed to change this password again. A PCM which has been previously installed in another vehicle will have learned the other vehicle's fuel continue password and will require a learn procedure after programming to learn the current vehicle's password.

To program the theft deterrent password, see THEFT DETERRENT PASSWORD LEARN PROCEDURE under PROGRAMMING in SELF-DIAGNOSTICS - 4.8L, 5.3L & 6.0L "C" & "K" SERIES TRUCKS article.

DRIVE CYCLES

See INSPECTION/MAINTENANCE SYSTEM CHECK .

SUMMARY

If no Diagnostic Trouble Codes (DTC) are present and a no-start condition exists, proceed to appropriate BASIC DIAGNOSTIC PROCEDURES article. If no DTCs are present and a driveability condition exists, proceed to appropriate TROUBLE SHOOTING - NO CODES article for diagnosis by symptom (i.e., ROUGH IDLE, NO-START, etc.).

MIL INOPERATIVE

Note. For circuit reference, see WIRING DIAGRAMS article. For component locations, see COMPONENT LOCATIONS . For connector identification, see CONNECTOR IDENTIFICATION .

MIL ALWAYS ON