Engine Control Module: Description and Operation
Engine Control Module (ECM) Removal/Install:
The ECM is located in the left side of engine compartment attached to the left inner fender behind the battery. The ECM also incorporates the barometric pressure sensor in it's housing.
The ECM has been programmed to monitor different circuits of the diesel fuel injection system. This monitoring is called on-board diagnostics. Certain criteria must be met for a diagnostic trouble code to be entered into the ECM memory. The criteria may be a range of engine rpm, engine temperature, time or other input signals to the ECM. If all of the criteria for monitoring a system or circuit are met, and a problem is sensed, then a DTC will be stored in the ECM memory. It is possible that a DTC for a monitored circuit may not be entered into the ECM memory, even though a malfunction has occurred. This may happen when the monitoring criteria have not
been met. The ECM compares input signal voltages from each input device with specifications (the established high and low limits of the input range) that are programmed into it for that device. If the input voltage is not within the specifications and other trouble code criteria are met, a DTC will be stored in the ECM memory.
ECM OPERATING MODES
As input signals to the ECM change, the ECM adjusts its response to the output devices. For example, the ECM must calculate a different fuel quantity and fuel timing for engine idle condition than it would for a wide open throttle condition. There are several different modes of operation that determine how the ECM responds to the various input signals.
Ignition Switch On (Engine Off)
When the ignition is turned on, the ECM activates the glow plug relay for a time period that is determined by engine coolant temperature, atmospheric temperature and battery voltage.
Engine Start-Up Mode
The ECM uses the engine temperature sensor and the crankshaft position sensor (engine speed) inputs to determine fuel injection quantity.
Normal Driving Modes
Engine idle, warm-up, acceleration, deceleration and wide open throttle modes are controlled based on all of the sensor inputs to the ECM. The ECM uses these sensor inputs to adjust fuel quantity and fuel injector timing.
Limp-In Mode
If there is a fault detected with the accelerator pedal position sensor, the ECM will set the engine speed at 1100 RPM.
Overspeed Detection Mode
If the ECM detects engine RPM that exceeds 5200 RPM, the ECM will set a DTC in memory and illuminate the MIL until the DTC is cleared.
After-Run Mode
The ECM transfers RAM information to ROM and performs an Input/Output state check.
MONITORED CIRCUITS
The ECM is able to monitor and identify most driveability related trouble conditions. Some circuits are directly monitored through ECM feedback circuitry. In addition, the ECM monitors the voltage state of some circuits and compares those states with expected values. Other systems are monitored indirectly when the ECM conducts a rationality test to identify problems. Although most subsystems of the engine control module are either directly or indirectly monitored, there may be occasions when diagnostic trouble codes are not immediately identified. For a trouble code to set, a specific set of conditions must occur and unless these conditions occur, a DTC will not set.
DIAGNOSTIC TROUBLE CODES
Each diagnostic trouble code (DTC) is diagnosed by following a specific procedure. The diagnostic test procedure contains step-by-step instruction for determining the cause of the DTC as well as no trouble code problems.
HARD CODE
A DTC that comes back within one cycle of the ignition key is a hard code. This means that the problem is current every time the ECM/SKIM checks that circuit or function. Procedures in this manual verify if the DTC is a hard code at the beginning of each test. When the fault is not a hard code, an intermittent test must be performed.
NOTE: If the scan tool displays faults for multiple components (i.e. ECT, VSS, IAT sensors) identify and check the shared circuits for possible problems before continuing (i.e. sensor grounds or 5-volt supply circuits). Refer to the appropriate schematic to identify shared circuits.
INTERMITTENT CODE
A DTC that is not current every time the ECM/ SKIM checks the circuit or function is an intermittent code. Most intermittent DTCs are caused by wiring or connector problems. Problems that come and go like this are the most difficult to diagnose;they must be looked for under specific conditions that cause them.
NOTE: Electromagnetic (radio) interference can cause an intermittent system malfunction. This interference can interrupt communication between the ignition key transponder and the SKIM.
The following checks may assist you in identifying a possible intermittent problem:
- Visually inspect the related wire harness connectors. Look for broken, bent, pushed out, loose fitting or corroded terminals.
- Visually inspect the related wire harness. Look for chafed, pierced or partially broken wire.
- Refer to hotlines or technical service bulletins that may apply.
ECM DIAGNOSTIC TROUBLE CODES
IMPORTANT NOTE: Before replacing the ECM for a failed driver, control circuit or ground circuit, be sure to check the related component/circuit integrity for failures not detected due to a double fault in the circuit. Most ECM driver/control circuit failures are caused by internal failures to components (i.e. relays and solenoids) and shorted circuits (i.e. sensor pull-ups, drivers and ground circuits). These faults are difficult to detect when a double fault has occurred and only one DTC has set. If the scan tool displays faults for multiple components (i.e.VSS, ECT, Batt Temp, etc.) identify and check the shared circuits for possible problems before continuing (i.e. sensor grounds or 5-volt supply circuits). Refer to the appropriate wiring diagrams to identify shared circuits.
STANDARD PROCEDURE - PCM/ECM/SKIM PROGRAMMING - DIESEL
NOTE: Before replacing the PCM/ECM for a failed driver, control circuit or ground circuit, be sure to check the related component/circuit integrity for failures not detected due to a double fault in the circuit. Most PCM/ECM driver/control circuit failures are caused by internal component failures (i.e. relay and solenoids) and shorted circuits (i.e. pull-ups, drivers and switched circuits). These failures are difficult to detect when a double fault has occurred and only one DTC has set.
PCM/SKIM PROGRAMMING
When a PCM (JTEC) and the SKIM are replaced at the same time perform the following steps in order:
1. Program the new PCM (JTEC)
2. Program the new SKIM
3. Replace all ignition keys and program them to the new SKIM.
ECM/SKIM PROGRAMMING
When an ECM (Bosch) and the SKIM are replaced at the same time perform the following steps in order:
1. Program the new SKIM
2. Program the new ECM (Bosch)
PROGRAMMING THE ECM (Bosch)
1. To program the VIN, connect the DRB III(R) and turn the ignition on.
2. Select Engine from the main menu. The DRB III(R) will require the VIN to be entered before continuing.
3. Select ENTER to update the VIN. The DRB III(R) will display the updated VIN.
4. If the engine is equipped with air conditioning, the ECM A/C function must be enabled. Enable the ECM A/C function as follows:
- Using the DRB III(R) select ENGINE, MISCELLANEOUS, then ENABLE/DISABLE A/C
- Push 1 to enable A/C. DRB III(R) screen should display A/C Activated.
PROGRAMMING THE PCM (JTEC)
The SKIS Secret Key is an ID code that is unique to each SKIM. This code is programmed and stored in the SKIM, PCM and transponder chip (ignition keys). When replacing the PCM it is necessary to program the secret key into the new PCM using the DRB III(R). Perform the following steps to program the secret key into the PCM.
1. Turn the ignition switch on (transmission in park/neutral).
2. Use the DRB III(R) and select THEFT ALARM, SKIM then MISCELLANEOUS.
3. Select PCM REPLACED (GAS ENGINE).
4. Enter secured access mode by entering the vehicle four-digit PIN.
5. Select ENTER to update PCM VIN.
NOTE: If three attempts are made to enter secure access mode using an incorrect PIN, secured access mode will be locked out for one hour. To exit this lockout mode, turn the ignition to the RUN position for one hour then enter the correct PIN. (Ensure all accessories are turned off. Also monitor the battery state and connect a battery charger if necessary).
6. Press ENTER to transfer the secret key (the SKIM will send the secret key to the PCM).
7. Press Page Back to get to the Select System menu and select ENGINE, JTEC (diesel only), MISCELLANEOUS, and SRI MEMORY CHECK.
8. The DRB III(R) will ask, Is odometer reading between XX and XX? Select the YES or NO button on the DRB III(R). If NO is selected, the DRB III(R) will read, Enter odometer Reading
PROGRAMMING THE SKIM
1. Turn the ignition switch on (transmission in park/neutral).
2. Use the DRB III(R) and select THEFT ALARM, SKIM then MISCELLANEOUS.
3. Select PCM REPLACED (GAS ENGINE).
4. Program the vehicle four-digit PIN into SKIM.
5. Select COUNTRY CODE and enter the correct country.
NOTE: Be sure to enter the correct country code. If the incorrect country code is programmed into SKIM, the SKIM must be replaced.
6. Select YES to update VIN (the SKIM will learn the VIN from the PCM).
7. Press ENTER to transfer the secret key (the PCM will send the secret key to the SKIM).
8. Program ignition keys to SKIM.
NOTE: If the PCM and the SKIM are replaced at the same time, all vehicle keys will need to be replaced and programmed to the new SKIM.
PROGRAMMING IGNITION KEYS TO THE SKIM
1. Turn the ignition switch on (transmission in park/neutral).
2. Use the DRB III(R) and select THEFT ALARM, SKIM then MISCELLANEOUS.
3. Select PROGRAM IGNITION KEY'S.
4. Enter secured access mode by entering the vehicle four-digit PIN.
NOTE: A maximum of eight keys can be learned to each SKIM. Once a key is learned to a SKIM it (the key) cannot be transferred to another vehicle.
If ignition key programming is unsuccessful, the DRB III(R) will display one of the following messages:
Programming Not Attempted - The DRB III(R) attempts to read the programmed key status and there are no keys programmed into SKIM memory.
Programming Key Failed (Possible Used Key From Wrong Vehicle) - SKIM is unable to program key due to one of the following:
- faulty ignition key transponder
- ignition key is programmed to another vehicle.
8 Keys Already Learned, Programming Not Done -SKIM transponder ID memory is full.
5. Obtain ignition keys to be programmed from customer (8 keys maximum).
6. Using the DRB III(R), erase all ignition keys by selecting MISCELLANEOUS and ERASE ALL CURRENT IGN.KEYS.
7. Program all ignition keys. Learned Key In Ignition - Ignition key transponder ID is currently programmed in SKIM memory.