Diesel On Board Diagnostics II System

DIESEL ON BOARD DIAGNOSTICS SYSTEM

Overview

The California Air Resources Board (CARB) began regulation of On Board Diagnostic (OBD) for diesel vehicles sold in California beginning with the 1997 model year. OBD requires monitoring of emission-related components. The Malfunction Indicator Lamp (MIL) is required to light and alert the driver of a malfunction and the need for service of the emission control system. A Diagnostic Trouble Code (DTC) is associated with the MIL identifying the specific area of the fault.

Note: The OBD system is used on California vehicles under 14,000 GVW.

The OBD system meets government regulations by monitoring the emission control system. When a system or component exceeds emission thresholds or a component operates outside of tolerance, a Diagnostic Trouble Code (DTC) will be stored and the Malfunction Indicator Lamp (MIL) will be illuminated.

The OBD Monitors detect system faults and initiates DTC setting and MIL activation. Fault detection strategy and MIL operation are associated with drive cycles. An OBD pending DTC is stored in the PCM keep alive random access memory when a fault is first detected. The MIL is turned on after two consecutive drive cycles with faults. The DTC is cleared after 40 engine warm-up cycles without the fault being detected once the MIL is turned off. Once a Monitor turns on the MIL, it will require three consecutive drive cycles without a fault for the MIL to turn off. The operation of each of the OBD Monitors is discussed in detail within this section.

The On Board diagnostic computer program in the electronic Powertrain Control Module (PCM) coordinates the OBD self-monitoring system. This program controls all the monitors and interactions, DTC and MIL operation, Freeze Frame data and scan tool interface.

Freeze Frame data describes stored engine conditions such as state of the engine rpm and load at the point the first fault is detected. This data is accessible with the scan tool to assist in repairing the vehicle.

OBD Inspection Maintenance (IM) Readiness DTC P1000 indicates that not all of the OBD monitors have been completed since the PCMs keep alive random access memory was last cleared. In some states, it may not be possible to obtain vehicle registration if P1000 is detected during inspection. To erase DTC P1000 from the PCM, operate the vehicle until the DTC is cleared using the manufacturer's specified drive cycle.

The On Board Diagnostic System is comprised of the Comprehensive Component Monitor, Glow Plug Monitor, Misfire Detection Monitor and Exhaust Gas Recirculation Monitor.

Diesel On Board Diagnostics Monitors

This section provides a general description of each OBD monitor. In these descriptions, the monitor strategy, hardware, testing requirements and methods are presented together to provide an overall understanding of each monitor operation.

Each illustration depicts the Powertrain Control Module (PCM) as the main focus with the primary inputs and outputs for each monitor. The numbers to the left of the PCM represent the inputs used by each of the monitor strategies to enable or activate the monitor. The components and subsystems to the right of the PCM represent the hardware and signals used while performing the tests and the systems being tested.

Comprehensive Component Monitor illustration has numerous components and signals involved and is shown generically. When referring to the illustrations, match the numbers to the corresponding numbers in the monitor descriptions for a better comprehension of the monitor and associated Diagnostic Trouble Codes (DTCs).

These monitor descriptions are intended as general information only.

Deviations From Standard Gasoline Implementation of OBD

1. Readiness (i.e.: all monitors complete) is based on diagnostics for the following 6.0L diesel engine systems:

- Comprehensive Component Monitor (CCM)
- Misfire Detection Monitor
- EGR Monitor

The glow plug monitor is part of the comprehensive component monitor.

Readiness is based on every OBD (component) having run sufficiently to have found a fault without regard to whether or not a fault exists.

2. The drive cycle provided in Section 2 is used to clear a P1000 code. The diesel differs substantially from the gasoline system.

3. The command to clear DTCs will ONLY clear P1000 if all drive cycle testing has been satisfied. All other detected DTCs will be cleared with a CLEAR code command from the scan tool if the fault that caused the DTC is no longer present.

Comprehensive Component Monitor

Comprehensive Component Monitor:

The Comprehensive Component Monitor (CCM) is an on-board strategy designed to monitor a fault in any electronic component or circuit that provides input or output signal to the Powertrain Control Module (PCM) and is not exclusively monitored by another monitor system. Inputs and outputs are considered inoperative when a failure exists due to a lack of circuit continuity, out-of-range value, or a failed rationality check.

The CCM covers many components and their circuits. The tests vary depending on the hardware, function, and type of signal. For example, analog inputs are typically checked for opens, shorts, out of range values and rationality. This type of monitoring is performed continuously. These tests may require the monitoring of several components and can only be performed under the appropriate test conditions. Some outputs are also monitored for the correct function by observing the reaction of the control system to a given change in the output command. An example of this would be the Injection Control System.

In general, the CCM covers a broad range of individual component and circuit checks and testing is performed under various conditions. The CCM is enabled after the ignition switch is turned on for three seconds. Certain conditions are required before some components can be tested totally complete. A Diagnostic Trouble Code (DTC) is stored in continuous memory when a fault is determined, and the Malfunction Indicator Lamp (MIL) is activated if the fault detected affects emissions. All of the CCM Monitor tests are also performed during on demand self-test.

The following is an example of some of the input and output components monitored by the CCM. The components monitored may belong to the engine, transmission or any other PCM supported subsystem.

1. Inputs:

Engine Oil Temperature (EOT), Accelerator Pedal Position (APP), Camshaft Position (CMP)

2. Outputs:

Injection Pressure Regulator (IPR), Exhaust Gas Recirculation (EGR) Valve

3. The MIL is activated after a fault is detected, if the fault detected affects emissions.

Misfire Detection Monitor

The misfire detection monitor is an on-board strategy designed to monitor engine misfire and identify the specific cylinder in which the misfire has occurred. Misfire is defined as lack of combustion in a cylinder due to poor compression, fuel delivery or mechanical engine failure. The misfire detection monitor will be enabled only when certain base engine conditions are first satisfied. Input from the following sensors is required to enable the monitor: Engine Oil Temperature (EOT), Crankshaft Position (CKP), Mass Fuel Desired (MFDES), Intake Air Temperature (IAT), Fuel Level (FLI) and Injector Control Pressure (ICP).

1. The CKP signal generated is the main input used in determining cylinder misfire.

2. The input signal generated by the CKP sensor is derived by sensing the passage of the teeth from the crankshaft position wheel, which is mounted on the crankshaft.

3. The input signal to the PCM is then used to calculate the time between CKP edges and also crankshaft rotational velocity and acceleration. By comparing the accelerations of each cylinder event, the power loss of each cylinder is determined. When the power loss of a particular cylinder is sufficiently less than a calibrated value and other criteria is met, the suspect cylinder is determined to have misfired.

Misfire Type B:

Upon detection of a misfire type B (1,000 revolutions), which will exceed the emissions threshold or cause a vehicle to fail an inspection and maintenance tailpipe emissions test, the MIL will illuminate and a DTC will be stored.

DTC P0300 - P0308:

The DTC associated with multiple cylinder misfire is DTC P0300.

The DTCs associated with cylinder misfire are P0301, P0302, P0303, P0304, P0305, P0306, P0307 and P0308.

Glow Plug Monitor

Glow Plug System:

The 6.0L diesel engine utilizes a Glow Plug Monitor (GPM) system designed to detect failed glow plugs or failed wiring in the glow plug system. Diagnostic Trouble Codes (DTCs) indicate which cylinder has failed glow plugs or failed glow plug wiring.

The glow plug system is composed of a solid state Glow Plug Control Module (GPCM), glow plugs and the associated wiring harness. The glow plug on-time is controlled by the Powertrain Control Module (PCM) and is a function of oil temperature, barometric pressure and battery voltage. The PCM enables the GPCM which drives the individual glow plugs. Glow plug on-time, varies between 1 to 120 seconds. In addition to the PCM control, the GPCM limits the glow plug operation to 180 seconds regardless of PCM commanded ontime. The power to the glow plugs is provided through the GPCM solid state drivers directly from the vehicle battery. The GPCM monitors and detects individual glow plug functionality, and the control and communication links to the PCM. The failures detected by the GPCM are passed to the PCM using a serial communication signal on the diagnostic line.

Note: Wait-to-start lamp on time is controlled by the PCM and is independent from GPCM on-time.

The Key On Engine Off (KOEO) test is performed in order to test the GPCM control circuit for failure. Glow plugs are not operated during this test.

The Glow Plug Monitor Self Test is a functional KOER test of the Powertrain Control Module (PCM) performed on demand with the engine running and the A/C off. The PCM will activate the GPCM which monitors the glow plugs. The pedal may be used to increase the engine speed to increase voltage if needed. A fault must be present at the time of testing for the test to detect a fault. The DTCs will be sent to the PCM on the diagnostic line and output to the scan tool.

Glow Plug Monitor:

The following is an example of some of the input and output components monitored by the GP monitor. The components monitored belong to the engine system.

1. Inputs:

Engine Oil Temperature (EOT), Barometric Pressure Sensor (BARO)

2. Outputs:

Glow Plug Control Module (GPCM)

3. The MIL is activated after a fault, if the fault detected affects emissions.