Feedback Carburetor Tests W/codes GMC Vandura I

DIAGNOSIS & TESTING

CCC system diagnosis should be done in the following order

1. Ensure that all engine systems NOT related to CCC are fully operational. DO NOT proceed with testing until all other systems have been checked and/or repaired as needed.
2. Enter diagnostic mode and record trouble codes flashed by "CHECK ENGINE" light. Exit diagnostic mode.
3. Distinguish between "hard" and "intermittent" trouble codes.
4. If trouble codes were displayed, go to Diagnostic Circuit Check chart. Follow instructions given there.
5. If no trouble codes were recorded, go to Driver Complaint Sheet and follow instructions given there.
6. After any repairs are made, perform System Performance Check. Clear any trouble codes.

RECALLING TROUBLE CODES

The ECM stores component failure information under related trouble codes which can be recalled for diagnosis and repair. When recalled, these codes will be displayed by flashes of the "CHECK ENGINE" light. Codes are displayed starting with the lowest numbered code. Only codes in which a related malfunction has occurred will be displayed.

Codes are called out by flashes of the "CHECK ENGINE" light. For example, "FLASH", "FLASH", "FLASH", pause, "FLASH", "FLASH", followed by a longer pause, identifies trouble code "32". First series of flashes indicates first digit of trouble code; second series of flashes indicates second digit of trouble code.

Scheme 138

1. Turn ignition switch to "ON" position. "CHECK ENGINE" light should come on. Locate Assembly Line Data Link (ALDL) connector attached to ECM wiring harness under instrument panel. Connector is located under center of instrument panel on "S" series trucks, and on left side of instrument panel on all other models. (Scheme 138) Insert jumper wire from terminal "A" to "B" (12-pin ALDL) or terminal "D" to "E" (5-pin ALDL). (Scheme 138): ALDL Connector Terminal Locations Jumper test terminal to ground terminal.
2. "CHECK ENGINE" light should flash code "12". Code "12" consists of a "FLASH", pause, "FLASH", "FLASH". A longer pause will follow, then code "12" will repeat 2 more times. This check indicates that the self-diagnostic system is working. After code "12" displays 3 times, any other trouble codes stored in the ECM memory will be displayed.
3. If more than one code is stored, they will be displayed from the lowest numbered code to the highest. Each code will flash 3 times. After all codes have been displayed, the complete cycle will repeat. Repetition of cycle continues as long as the "TEST" terminal of ALDL connector is grounded.

ECM Terminal Identification All terminals are not used in all applications. Scheme 139

CLEARING TROUBLE CODES

To clear memory of trouble codes, turn ignition "OFF" and remove "ECM" fuse for 10 seconds. On "S" series trucks, fuse is located in engine compartment, at center of vehicle. On all other models, fuse is located at upper right corner of fuse block.

EXITING DIAGNOSTIC MODE

To exit diagnostic mode, turn ignition "OFF", then remove jumper wire from ALDL connector.

Note. The terms "enter diagnostics" and "exit diagnostics" will be used periodically throughout this section. Follow appropriate procedure for entering and exiting diagnostic mode when instructed to do so.

FAILURE CODE DETERMINATION

During any diagnostic procedure, "hard failure" codes MUST be distinguished from "intermittent failure" codes. Diagnostic charts CANNOT be used to analyze "intermittent failure" codes, except as noted under Diagnostic Procedure. To determine "hard failure" codes and "intermittent failure" codes, proceed as follows

1. Turn ignition "ON" and enter diagnostics. Read and record all stored trouble codes. Exit diagnostics and clear trouble codes.
2. Apply parking brake and place manual transmission in neutral, or automatic transmission in "P" (park). Block drive wheels. Start engine. "CHECK ENGINE" light should go out. Run warm engine at specified curb idle for 5 minutes and note "CHECK ENGINE" light. NOTE: Grounding "TEST" terminal with engine running will force engine to operate in closed loop mode if engine is warm and oxygen sensor is hot. If "CHECK ENGINE " light does not glow while in closed loop, CCC system is operating properly.
3. If "CHECK ENGINE" light comes on, enter diagnostics. Read and record trouble codes. These are "hard failure" codes. Codes "13", "15", "24", "35", "44", "45" and "55" may require road test to reset "hard failure" after trouble codes were cleared.
4. If "CHECK ENGINE" light does not come on, all stored trouble codes were "intermittent failures", except as noted under Diagnostic Procedure.

Note. Trouble codes "13", "24", "44" and "45" require at least 5 minutes engine operation at part throttle before trouble codes will store in memory.

DIAGNOSTIC PROCEDURE

The CCC system may be considered a possible source of engine performance, fuel economy and exhaust emission problems, ONLY after normal checks (those which apply to vehicles without CCC) have been performed.

Diagnosis of CCC system consists of 3 types of check sheets: Diagnostic Circuit Check, Driver Complaint Sheet and System Performance Check. Any check sheet may refer to another chart for locating source of problem, or indicate no problem and refer to another sheet.

If all check sheets refer to others, problem is not in CCC system. The check sheets and their procedures are as follows

Note. If vehicle exhibits performance problems and no codes are set, refer to System Performance Chart. Components recorded by trouble codes are generally not the source of performance problems when no codes are stored in ECM memory.

DIAGNOSTIC CIRCUIT CHECK

This check ensures that the self-diagnostic system is working, determines that the trouble codes will display and guides diagnosis to other problem areas. Use this test if complaint is "CHECK ENGINE" light related, while noting the following

1. If code "51" is displayed, refer to PROM removal and installation in this article for diagnosis of code.
2. If codes "51", "54" or "55" are displayed in addition to other code(s), refer to diagnostic chart for "50" series code first, then go to lowest numbered code.

DRIVER COMPLAINT SHEET

1. If complaint is not "CHECK ENGINE" light related, this check will lead to most likely problem area. However, before beginning procedure, make checks that would normally be made for a similar complaint on a vehicle without CCC system.
2. Follow instructions in diagnostic chart and repair malfunction. After repair, perform System Performance Check.

SYSTEM PERFORMANCE CHECK

1. This check verifies that CCC system is functioning correctly. This check should be made after any repair on CCC system.
2. When performing check, always engage parking brake and block drive wheels. On engines equipped with Varajet carburetors (E2SE model), disconnect bowl vent at carburetor. Reconnect after check is complete.
3. In some cases, the oxygen sensor will cool off while engine is idling. This causes engine to enter open loop mode. To restore closed loop mode, run engine at fast idle for several minutes to heat oxygen sensor.

Note. Although there are many charts connected with CCC diagnosis, only 2 are needed to prove proper system operation. Normally, only 3 charts are necessary to find an existing problem.

DIAGNOSTIC TOOLS REQUIRED

1. CCC system testing requires a dwell meter, tachometer, test light, ohmmeter, digital voltmeter (with 10 megohm minimum resistance), vacuum pump, vacuum gauge and jumper wires.
2. Jumper wires are used to by-pass a circuit and to insert between special connectors. Using proper terminals, make jumper wires approximately 6" long. One wire should have male connectors at both ends, 2 should have female connectors at both ends, and the others should be male at one end and female at the other.
3. The dwell meter is used to check mixture control (M/C) solenoid operation. It must be set on 6-cylinder scale. Connect positive dwell meter lead to bright green connector near M/C solenoid and negative lead to ground. DO NOT connect any other equipment to this lead. DO NOT allow lead to contact any ground source, including rubber hoses. NOTE: If engine operation changes when dwell meter is connected, remove it and try a different meter. Some brands of meters affect system operation.
4. When engine is at operating temperature and idling, dwell meter needle will fluctuate between 10° and 50°. This indicates closed loop operation. If the needle does not move, open loop operation is indicated.

ECM TROUBLE CODE ID

ECM TROUBLE CODE IDENTIFICATION

ENGINE PERFORMANCE PROBLEM - ODOR, SURGE, FUEL ECONOMY OR EMISSION PROBLEM

1. If the "CHECK ENGINE" light is not on, normal checks that would be performed on cars without the system should be done first.
2. If the alternator or coolant light is on with the "CHECK ENGINE" light, they should be diagnosed first.
3. Inspect for poor connections at coolant sensor, mixture control solenoid, etc. Also check for poor or loose vacuum hoses and connections. Repair as necessary.
4. If there is an intermittent "CHECK ENGINE" light, but no trouble code is stored, check the following: Check ignition coil to ground and check for arcing at spark plug wires or spark plugs Check battery-to-ECM terminals"C" and "R". Check ECM Terminals "A" and "U" to ground. Check ECM Terminal No. 19 to distributor, including tach filter. Check for a loss of trouble code long-term memory memory. Grounding the dwell lead for 10 seconds with the "TEST" lead ungrounded should produce a Code 23. This Code 23 should remain after engine is turned off and ignition switch is turned to the "RUN" position. If not, ECM is defective and must be replaced. Check that the EST wires are kept away from spark plug wires, distributor housing, ignition coil and alternator. Wires from ECM Terminal No. 13 to distributor and the shield around the EST wires should have a good ground. Check for an open diode across the A/C compressor clutch.
5. If the customer complaint is detonation (spark knock), check the vacuum sensor output. See VACUUM SENSOR OUTPUT TEST. Also check TPS enrichment operation. See TPS ENRICHMENT CHECK flow chart.
6. If the complaint is poor performance and/or fuel economy, perform CODE 42 - EST CKT CHECK.
7. If the customer is experiencing poor full throttle performance, refer to CODE 21 - TPS CKT CHECK.
8. If the complaint is intermittent no-start, check for incorrect pick-up coil or ignition coil. See CRANKS, BUT WON'T RUN flow chart. Also check for intermittent ground connections on the ECM.

ALL OTHER COMPLAINTS

For any other complaints, do the SYSTEM PERFORMANCE CHECK with engine warmed to normal operating temperature.

Flow Chart - Diagnostic Circuit Check. Scheme 140

Flow Chart - Diagnostic Circuit Check (1 Of 2). Scheme 141

Flow Chart - Diagnostic Circuit Check (2 Of 2). Scheme 142

Flow Chart - System Performance Check. Scheme 143

Flow Chart - System Performance Check. Scheme 144

Flow Chart - Dwell Fixed Under 10 Degrees. Scheme 145

Flow Chart - Dwell Fixed Under 10 Degrees. Scheme 146

Flow Chart - Dwell Fixed Between 10-50 Degrees. Scheme 147

Flow Chart - Dwell Fixed Between 10-50 Degrees. Scheme 148

Flow Chart - Dwell Fixed Over 50 Degrees. Scheme 149

Flow Chart - Dwell Fixed Over 50 Degrees. Scheme 150

Flow Chart - TPS Enrichment Check. Scheme 151

Flow Chart - TPS Enrichment Check. Scheme 152

Flow Chart - "Check Engine" Light Inoperative. Scheme 153

Flow Chart - "Check Engine" Light Inoperative. Scheme 154

Flow Chart - Won't Flash Code 12, (Remote Lamp Driver In Harness). Scheme 155

Flow Chart - Won't Flash Code 12, (Remote Lamp Driver In Harness) (1 Of 2). Scheme 156

Flow Chart - Won't Flash Code 12, (Remote Lamp Driver In Harness) (2 Of 2). Scheme 157

Flow Chart - Electric Diverter Valve (EDV) Check. Scheme 158

Flow Chart - Electric Diverter Valve (EDV) Check. Scheme 159

Flow Chart - Vacuum Sensor Output Check. Scheme 160

Flow Chart - Vacuum Sensor Output Check. Scheme 161

Flow Chart - Canister Purge Valve Check (5.0L & 5.7L Only). Scheme 162

Flow Chart - Canister Purge Valve Check (5.0L & 5.7L Only). Scheme 163

Flow Chart - Divert Valve Check (4.lL Cab & Chassis Only). Scheme 164

Flow Chart - Divert Valve Check (4.lL Cab & Chassis Only) (1 Of 2). Scheme 165

Flow Chart - Divert Valve Check (4.lL Cab & Chassis Only) (2 Of 2). Scheme 166

Flow Chart - Torque Converter Clutch (TCC) Elec Diagnosis. Scheme 167

Flow Chart - Torque Converter Clutch (TCC) Elec Diagnosis. Scheme 168

Flow Chart - EST Performance Check. Scheme 169

Flow Chart - EST Performance Check. Scheme 170

Flow Chart - Engine Cranks, But Will Not Run (Integral Coil). Scheme 171

Note. Perform Diagnostic Circuit Check before using this procedure. If a tachometer is connected to the tachometer terminal, disconnect it before proceeding with the test. Intermittent no start may be caused by wrong pick-up or ignition coil.

Flow Chart - Engine Cranks, But Will Not Run (Integral Coil) (1 Of 2). Scheme 172

Flow Chart - Engine Cranks, But Will Not Run (Integral Coil) (2 Of 2). Scheme 173

Flow Chart - Engine Cranks, But Will Not Run (External Coil). Scheme 174

Note. Perform Diagnostic Circuit Check before proceeding with this test. If a tachometer is connected to the tachometer terminal, disconnect before proceeding with the test.

Flow Chart - Engine Cranks, But Will Not Run (External Coil) (1 Of 2). Scheme 175

Flow Chart - Engine Cranks, But Will Not Run (External Coil) (2 Of 2). Scheme 176

Flow Chart, Code 12 - No Distributor Reference Signal To ECM. Scheme 177

Flow Chart - Code 12 - No Distributor Reference Signal To ECM. Scheme 178

Flow Chart, Code 13 - Oxygen (O2) Sensor Circuit. Scheme 179

Flow Chart - Code 13 - Oxygen (O2) Sensor Circuit. Scheme 180

Flow Chart, Code 14 - Shorted Coolant Temp. Sensor (CTS) Ckt. Scheme 181

Flow Chart - Code 14 - Shorted Coolant Temp. Sensor (CTS) Circuit. Scheme 182

Flow Chart, Code 15 - Open Coolant Temp. Sensor (CTS) Circuit. Scheme 183

Flow Chart - Code 15 - Open Coolant Temp. Sensor (CTS) Circuit. Scheme 184

Flow Chart, Code 21 - Throttle Position Switch (TPS) Circuit. Scheme 185

Flow Chart, Code 21 - Throttle Position Switch (TPS) Circuit. Scheme 186

Flow Chart, Code 23 - Open or Grounded Mixt Control Sol Circuit. Scheme 187

Flow Chart, Code 23 - Open or Grounded Mixture Control Solenoid Circuit. Scheme 188

Flow Chart, Code 34 - Vacuum Sensor Circuit. Scheme 189

Note. Check for over 34 kPa (10" Hg) of vacuum at sensor with engine idling. If not OK, repair.

Flow Chart, Code 34 - Vacuum Sensor Circuit. Scheme 190

Flow Chart, Code 41 - No Distributor Reference Pulses at Specific Engine RPM. Scheme 191

Flow Chart, Code 41 - No Distributor Reference Pulses at Specific Engine RPM. Scheme 192

Flow Chart, Code 42 - EST or EST Bypass Circuit Grounded or Open. Scheme 193

Flow Chart, Code 42 - EST or EST Bypass Circuit Grounded or Open. Scheme 194

Flow Chart, Code 44 - Lean Oxygen (O2) Sensor Failure. Scheme 195

Note. If M/C solenoid does not click with ignition ON and TEST terminal grounded, and there is no code 23 or 54, check for sticking M/C solenoid.

Flow Chart, Code 44 - Lean Oxygen (O2) Sensor Failure. Scheme 196

Flow Chart, Code 45 - Rich Oxygen (O2) Sensor Failure. Scheme 197

Note. If M/C solenoid does not click with ignition ON and TEST terminal grounded, and there is no Code 23 or 54, check for sticking M/C solenoid. If Code 54 is present, go to Chart 54 first.

Flow Chart, Code 45 - Rich Oxygen (O2) Sensor Failure. Scheme 198

CODE 51 - FAULTY PROM

PROM is either installed incorrectly, defective, or wrong part number. Check for proper installation and application. If ok, replace PROM.

Flow Chart, Code 54 - Shorted Mix Control Sol or Faulty ECM. Scheme 199

Flow Chart, Code 54 - Shorted Mixture Control Solenoid or Faulty ECM. Scheme 200

Flow Chart, Code 55 - Grounded Voltage Reference, High Voltage On Oxygen Sensor Circuit or ECM. Scheme 201

Note. Check for corrosion at ECM edgeboard connector and terminals. If present, check for coolant sensor, windshield or heater core leaks. Repair leak, clean connector terminals and replace ECM. Also, check for 4-terminal EST harness being too close to electrical signals, such as spark plug wires, distributor housing, generator, etc.

Flow Chart, Code 55 - Grounded Voltage Reference, High Voltage On Oxygen Sensor Circuit or ECM. Scheme 202

CHART C1 - ECM REPLACEMENT CHECK CHART

In order to reduce incidents of repeat ECM failure, a revisedECM diagnostic procedure is available. Beginning in 1982, most ECMs are equipped with Integrated Circuits (IC) in place of separate transistors to operate various controlled components.

These ICs, called Quad-Drivers (QDR), have 4 separate outputs, meaning that each QDR can operate up to 4 different components. An inoperative QDR can result in ECM output becoming open or shorted to ground. Often, all 4 outputs of a QDR will fail, even if just one QDR circuit is faulty.

Refer to the following tables to determine which ECMs contain QDRs. Since this procedure is not applicable to ECMs which do not contain QDRs, those ECMs are not listed.

Performing the diagnostic flow chart will identify an inoperative QDR. Once the circuit is identified, it must be repaired to eliminate repeat ECM failure. This diagnostic procedure must be used when "Replace ECM" is the conclusion of any procedure.

ECM QDR IDENTIFICATION

ECM QDR IDENTIFICATION

ECM QDR IDENTIFICATION

ECM QDR IDENTIFICATION

ECM QDR IDENTIFICATION

Scheme 203

ELECTRONIC CONTROL MODULE (ECM) R & I

Note. The ECM is located under the passenger seat on "G" series models (vans). On all other models, the ECM is located inside the instrument panel, near the glove box.

Disconnect negative battery cable. Disconnect electrical connectors from ECM. Remove ECM mounting hardware. Remove ECM. Note that replacement ECM's are not supplied with a PROM. To install ECM, reverse removal procedure. Ensure ground strap is securely attached.

REMOVAL

1. Remove ECM. Remove sheet metal screw holding access cover closed, then remove acccess cover. Place blade of small, flat screwdriver at PROM carrier reference end between edge of opening in case and underside of protruding lip of carrier. Pry up side of carrier as far as possible.
2. Repeat procedure on other reference end lip. Grasp carrier with thumb and forefinger. Gently rock carrier from side to side while applying upward force and remove PROM.

Replacing PROM in Electronic Control Module. Scheme 204

INSTALLATION

1. Before installing new PROM, ensure part number agrees with that of removed PROM. Molded "half-round" depression of PROM must be installed at same end as "squared-off" symmetrical end of carrier. Make sure that PROM is centered in carrier.
2. Position carrier squarely over PROM socket with "squared-off" symmetrical end of carrier aligned with small notch in socket. Press down firmly on top of carrier while pressing down on body of PROM with narrow, blunt tool. Squarely seat PROM in socket by alternately pressing down on either end of PROM.
3. Replace access cover and install ECM. Reconnect electrical connectors and start engine. Enter diagnostics and check for trouble code "51". If trouble code "51" does not appear, PROM is correctly installed.
4. If code "51" does appear, PROM is not fully seated, is installed backwards, has bent pins, or is defective. Remove ECM and fully seat PROM. If pins are bent, remove PROM, straighten pins and reinstall. If pins break or crack during straightening process, replace PROM. If PROM is installed backwards, it must be replaced.

OXYGEN SENSOR R & I

When handling oxygen sensor, use care to keep connector and louvered end free of grease or other contanimants. DO NOT use cleaning solvents of any type. Disconnect negative battery cable. Disconnect electrical connector and any attaching hardware. Carefully remove oxygen sensor.

A new oxygen sensor is pre-coated with anti-seize compound. If same oxygen sensor is being installed, coat threads with anti-seize compound. Install oxygen sensor and torque to 30 ft. lbs. (41 N.m). Reconnect electrical connector and any attaching hardware.

VACUUM SENSOR R & I

Vacuum sensor is located in engine compartment. (Scheme 205), (Scheme 206), (Scheme 207), and (Scheme 208). Locate sensor. Remove electrical connector, then remove sensor. To install sensor, reverse removal procedure.

COOLANT TEMPERATURE SENSOR R & I

Partially drain radiator until coolant level is below sensor. Disconnect electrical connector from sensor. Remove sensor from block. Reverse removal procedure to install.

Component Locations ("C/K" Series Trucks With 4.1L Engine). Scheme 205

Component Locations ("C/K" Series Trucks With V8 Engines). Scheme 206

Component Locations ("G" Series Vans With 4.1L Engine). Scheme 207

Component Locations ("G" Series Vans With V8 Engines). Scheme 208

CCC Wiring Diagram for "C/K" Series Trucks & "G" Series Vans. Scheme 209