Locating ALDL/OBD connector for checking CEL codes '91

[esmartuek]

I have no idea where to begin looking, so far I've done all but dismantle the dash, I've gone to dealers, parts shops, etc. and confounded them all in our search for the elusive plug... does someone out there have any idea where I need to be pointing my attention?

[atfdmike]

Originally Posted by esmartuek

I have no idea where to begin looking, so far I've done all but dismantle the dash, I've gone to dealers, parts shops, etc. and confounded them all in our search for the elusive plug... does someone out there have any idea where I need to be pointing my attention?

It looks like the same location regardless of engine type. The codes may be slightly different, so if this is not your engine, post what you have for more help. Hope this helps
1991 Isuzu Truck Trooper II L4-2559cc 2.6L SOHC (4ZE1)

Vehicle Level Powertrain Management Computers and Control Systems Testing and Inspection Displaying & Reading Trouble Codes Displaying & Reading Trouble CodesIf a problem develops in a monitored system with the engine running, the "Check Engine" light will come "ON" and a trouble code will be stored in ECM memory. As long as a problem is present, the light will remain "ON" while the engine is running. If the problem is intermittent, the light will go out but a trouble code will be stored in ECM memory. As a bulb check, the "Check Engine" light will come "ON" with the ignition switched "ON" and the engine not running. If no codes are present, the light will go out upon starting the engine. If the light remains "ON," the system has detected a fault.

Refer to DIAGNOSTIC CIRCUIT CHECK for information on checking the function of the on-board diagnostic system.

ACCESSING TROUBLE CODES

"Check Engine" Light And Diagnostic Connector

To access trouble codes, a test lead (white wire) and ground lead (black wire) are branched from the wiring harness under the center console near the ECM. With the ignition "ON" connect these two leads together. The "Check Engine" light will begin to flash code 12. Code 12 consists of one flash, a short pause, then two flashes. After a longer pause, code 12 will repeat two more times. This check indicates that the on-board diagnostic system is functioning. If no other codes are present, the cycle will repeat until the ignition is switched "OFF."

Reading Trouble Codes

If trouble codes are stored in memory, the lowest number code will flash three times followed by the next higher code number until all stored codes have been displayed. The codes will then repeat in the same order until the test lead is disconnected. Code 14, for example, indicates a problem in the coolant sensor circuit.

CLEARING CODES FROM MEMORY

Fuse And ECM Harness Connections


CAUTION:To avoid component damage, be sure ignition is "OFF" when disconnecting or reconnecting power to the ECM.</B> The trouble code memory receives a continuous 12 volts even with the ignition "OFF." After displaying and recording any trouble codes or after making repairs, the ECM memory should be cleared by interrupting the power for at least 10 seconds. This is accomplished by temporarily removing the #6 fuse in the engine compartment fuse and relay block or by disconnecting the battery. Codes are cleared automatically whenever the 14 pin ECM harness is disconnected. After clearing codes, it may be necessary to reset electronic accessories such as digital clocks and radios.

INTERMITTENT "CHECK ENGINE" LIGHT

"Intermittent" means that the "Check Engine" light comes on at times but does not stay on. Since codes may or may not be stored, the use of diagnostic charts could result in replacement of good parts.

Most intermittent problems are caused by faulty electrical wiring or connections. Carefully check these potential causes:

1. Poor mating of connector halves or terminals not fully seated in connector body.
2. Deformed or damaged terminals. All connector terminals in problem circuit should be carefully reformed to increase contact tension.
3. Poor terminal-to-wire connection. This requires removing terminal from connector body to properly check.
4. Poor ground connections.
5. If a visual check does not find the source of the problem, the vehicle may be driven with a voltmeter connected to a suspect circuit. An abnormal voltage reading when the problem occurs indicates the problem may be in that circuit.

An intermittent "Check Engine" light with no stored code may be caused by:

1. Arcing at ignition coil, plug wires or spark plugs.
2. Faulty power supply main relay.
3. Poor power supply circuit connections.
4. "Check Engine" light wire to ECM shorted to ground (circuit 22).
5. Diagnostic test lead to ECM shorted to ground (circuit 24).
6. Poor ECM ground connections at intake manifold.
7. Electrical system interference caused by a defective relay, ECM driven solenoid or switch. These problems cause an electrical surge and normally occur when the faulty component is operated.
8. Improper installation of accessories such as lights, sound systems, alarms, etc.

TROUBLE CODE IDENTIFICATION


CODE 12Indicates that on-board diagnostics are functioning when diagnostic leads are connected and ignition is "ON" (engine not running). Code not stored in memory.CODE 13Oxygen sensor defective or open circuit.CODE 14Shorted coolant sensor circuit.CODE 15Open coolant sensor circuit.CODE 21Both idle and wide open throttle "ON" simultaneously in throttle valve switch.CODE 22Open or shorted starter signal circuit.CODE 23Shorted power transistor output terminal.CODE 25Open or shorted circuit for pressure regulator VSV.CODE 26Open or shorted circuit for canister VSV.CODE 27Open in ECM driver transistor for canister VSV.CODE 32EGR gas temperature sensor malfunction.CODE 33Open or shorted circuit in fuel injector harness, dropping resistor or inside ECM.CODE 34EGR gas temperature sensor or wiring faulty.CODE 35Ignition power transistor harness open circuit.CODE 41Crank angle sensor open circuit or faulty signal.CODE 43Throttle valve switch idle contact continuously "ON."CODE 44Lean signal from oxygen sensor.CODE 45Rich signal from oxygen sensor.CODE 51Abnormal ROM in ECM micro computer.CODE 52Abnormal RAM in ECM micro computer.CODE 53Open in ECM driver transistor for pressure regulator VSV.CODE 54Defective ignition power transistor or grounding system.CODE 61Shorted or broken air flow sensor hot wire.CODE 62Broken air flow sensor cold wire.CODE 63Open or shorted wiring or defective vehicle speed sensor.CODE 64Open in ECM driver transistor for fuel injectors.CODE 65Wide open throttle contact in throttle valve switch continually "ON."1991 Isuzu Truck Trooper II V6-2827cc 2.8L

Vehicle Level Powertrain Management Computers and Control Systems Testing and Inspection Displaying & Reading Trouble Codes Displaying & Reading Trouble CodesIf a problem develops in a monitored system with the engine running, the "Check Engine" light will come "ON" and a trouble code will be stored in ECM memory. As long as a problem is present, the light will remain "ON" while the engine is running. If the problem is intermittent, the light will go out but a trouble code will be stored in ECM memory. As a bulb check, the "Check Engine" light will come "ON" with the ignition switched "ON" and the engine not running. If no codes are present, the light will go out upon starting the engine. If the light remains "ON," the system has detected a fault.

If the diagnostic terminal is grounded with the engine running, the system enters Field Service mode and the "Check Engine" light will indicate whether it is in "Open Loop" or "Closed Loop." In "Open Loop," the light flashes two and one half times per second. In "Closed Loop," the light flashes once per second. If the system is running lean while in "Closed Loop," the light will stay "OFF" most of the time. Conversely, it will stay "ON" most of the time if the system is running rich. While in Field Service mode, the ECM will not store new trouble codes.

Refer to DIAGNOSTIC CIRCUIT CHECK for information on checking the function of the on-board diagnostic system. Note that many electronic engine control tests require the use of a "Scan" tool.

"SCAN" DATA
"Scan" Data


NOTE: Ensure that any "Scan" tool used is compatible with the vehicle system. Use of an incompatible tool could result in misdiagnosis and unnecessary parts replacement."Scan" data listed in the table may be used for comparison after completing the Diagnostic Circuit Check and finding the on-board diagnostics functioning properly with no trouble codes displayed. The "Typical Data Values" are an average recorded from normally operating vehicles and are intended to represent what the system would typically display. Only the parameters on this table are used for diagnosis. If a "Scan" tool reads other parameters, the values are not recommended by Isuzu for diagnostic use.

ACCESSING TROUBLE CODES
ALDL/DLC Connector

The "Check Engine" light displays trouble codes that are stored in ECM memory. To activate the Diagnostic mode, a special connector located in the center console is utilized. When the ALDL (assembly line diagnostic link) connector is jumpered between terminals "A" and "B" with the ignition "ON" and the engine not running, the light will flash any stored codes.

The first code to display should be code 12. This indicates that the self-diagnostics are functioning and is not a trouble code. The code 12 display is a flash followed by a short pause, then two flashes followed by a longer pause. If other codes are present, they will display in the same manner after code 12 has flashed three times. For example, the code 23 display is two flashes followed by a short pause, then three flashes followed by a longer pause. Each stored code is displayed three times, starting with the lowest in numerical order. Code 12 will repeat when all codes have shown. If no codes are stored, code 12 will display repeatedly until Diagnostic mode is exited by removal of the ALDL jumper wire. Remove the jumper wire before attempting to start the engine.

To allow checking circuits which may be difficult to energize without driving the vehicle and being under particular operating conditions, all ECM controlled relays and solenoids (except fuel pump relay) are energized in Diagnostic mode.

"Scan" tools also utilize the ALDL connector to access system diagnostic information. The use of a "Scan" tool is required to perform many of the tests under TROUBLE CODE COMPONENTS.

INTERMITTENT "CHECK ENGINE" LIGHT

"Intermittent" means that the "Check Engine" light may come on at times but does not stay on. Since codes may or may not be stored, the use of diagnostic charts could result in replacement of good parts.

Most intermittent problems are caused by faulty electrical wiring or connections. Carefully check these potential causes:

1. Poor mating of connector halves or terminals not fully seated in connector body.
2. Deformed or damaged terminals. All connector terminals in problem circuit should be carefully reformed to increase contact tension.
3. Poor terminal-to-wire connection. This requires removing terminal from connector body to properly check.
4. Poor ground connections.
5. If a visual check does not find the source of the problem, the vehicle may be driven with a voltmeter connected to a suspect circuit. An abnormal voltage reading when the problem occurs indicates the problem may be in that circuit. If wiring and connectors check okay and a code was stored for a circuit having a sensor (except codes 44 and 45), substitute a known good sensor and recheck.
6. Loss of ECM trouble code memory. To check, disconnect throttle position sensor and idle engine until "Check Engine" light comes "ON." Code 22 should be stored in memory for at least 10 seconds after ignition is turned "OFF." If not, the ECM is faulty.

An intermittent "Check Engine" light with no stored code may be caused by:

1. Arcing at ignition coil, plug wires or spark plugs.
2. EST wires should be routed away from spark plug wires, ignition system components and alternator.
3. Poor power supply circuit connections.
4. "Check Engine" light wire to ECM shorted to ground (circuit BLU/PNK 03).
5. Diagnostic test lead to ECM shorted to ground (circuit 451).
6. Poor ECM ground connections.
7. Electrical system interference caused by a defective relay, ECM driven solenoid or switch. These problems cause an electrical surge and normally occur when the faulty component is operated.
8. Improper installation of accessories such as lights, sound systems, alarms, etc.

ECM "QUAD-DRIVER" CHECK

A shorted solenoid, relay coil or harness will not damage the ECM, but will cause the circuit and controlled component to be inoperative. When the circuit fault is not present or has been repaired, the "quad-driver" will again operate in a normal manner due to its fault protected design. If a fault has been repaired in a "quad-driver" controlled circuit, the original ECM should be reinstalled and the circuit checked for proper operation. ECM replacement will not be necessary if the repaired circuit or component now operates correctly.

CLEARING CODES FROM MEMORY


CAUTION:To avoid component damage, be sure ignition is "OFF" when disconnecting or reconnecting power to the ECM.</B> After displaying and recording any trouble codes or after making repairs, the ECM memory should be cleared by interrupting the power for at least 30 seconds. This is accomplished by temporarily removing the ECM fuse in the fuse and relay block under the dash or by disconnecting the battery. Depending on how the vehicle is equipped, it may also be possible to interrupt ECM power at the positive battery terminal "pigtail" or with an inline fuse holder originating at the positive battery terminal. After clearing codes, it may be necessary to reset electronic accessories such as digital clocks and radios.

When using a "Scan" tool, codes are cleared in the same manner.

TROUBLE CODE IDENTIFICATION


CODE 13Oxygen sensor circuit openCODE 14Coolant temperature sensor circuit, high temperature indicated (low circuit resistance indicates grounded circuit to ECM or shorted sensor)CODE 15Coolant temperature sensor circuit, low temperature indicated (high circuit resistance indicates open circuit to ECM or open sensor)CODE 21Throttle position sensor circuit (signal voltage high)CODE 22Throttle position sensor circuit (signal voltage low)CODE 24Vehicle speed sensor circuitCODE 32EGR system failureCODE 33MAP sensor circuit (signal voltage high, low vacuum)CODE 34MAP sensor circuit (signal voltage low, high vacuum)CODE 42Electronic spark timing (EST) circuitCODE 43Electronic spark control (ESC) circuitCODE 44Oxygen sensor circuit (lean indication)CODE 45Oxygen sensor circuit (rich indication)CODE 51PROM error (faulty or incorrectly installed PROM or incorrect PROM for application)CODE 52CALPAK error (faulty or incorrect CALPAKCODE 54Fuel pump circuit (low voltage)CODE 55ECM error