Engine Controls - Tests W/codes - V6: Diagnosis Chevrolet Pickup C1500

SELF-DIAGNOSTIC SYSTEM

All vehicle are equipped with either an Electronic Control Module (ECM), Powertrain Control Module (PCM) or Vehicle Control Module (VCM). Unless specifically stated, references to ECM also apply to PCM or VCM equipped vehicles.

The ECM is equipped with a self-diagnostic system, which detects system failures or abnormalities. When a malfunction occurs, ECM will illuminate the SERVICE ENGINE SOON light located on instrument panel. This light is also referred to as the Malfunction Indicator Light (MIL). When malfunction is detected and MIL is turned on, a corresponding trouble code will be stored in ECM memory. To retrieve stored codes, see READING TROUBLE CODES or RETRIEVING CODES (NON-SCAN) . Malfunctions are recorded as HARD FAILURES or as INTERMITTENT FAILURES.

DIAGNOSTIC PROCEDURE

Diagnosis of the computerized engine control system should be performed in the following order

1. Ensure all engine systems not related to the computer are operating properly. DO NOT proceed with testing unless all other problems have been repaired. Perform diagnostic circuit check before using trouble code charts. See BASIC TESTING article in this section.
2. If trouble codes were displayed (other than Code 12), determine whether codes are hard or intermittent. Hard codes cause Malfunction Indicator Light (MIL) to illuminate continuously with engine running. See «HARD OR INTERMITTENT TROUBLE CODE DETERMINATION»(ref-19444-S39668329352001010200000) . For diagnosing hard codes, proceed to appropriate trouble code chart. For diagnosing intermittent codes, proceed to INTERMITTENTS in TESTS W/O CODES article in this section. Exceptions are Code 13, 15, 24, 44 and 45 charts, which can help diagnose intermittent codes.
3. If trouble codes were not displayed and a driveability problem exists, refer to SYMPTOMS in TESTS W/O CODES article in this section. From there you will be sent to the appropriate area in SYSTEM/COMPONENT TESTS article in this section.
4. After repairs are made, clear trouble codes and perform FIELD SERVICE MODE CHECK in BASIC TESTING article in this section.

READING TROUBLE CODES

Note. Trouble codes retrieved from ECM/PCM/VCM may be related to either engine or transmission. For engine-related codes, use this article. For transmission-related codes, see G - TRANS. TESTS W/ CODES article in this section. To identify whether codes relate to transmission or engine, see TROUBLE CODE IDENTIFICATION table.

The ECM stores component failure information under a related trouble code which can be recalled for diagnosis and repair. Read trouble codes by counting Malfunction Indicator Light (MIL) flashes or with diagnostic scan tester connected to the Data Link Connector (DLC). The tester is faster, and capable of reading information which would require testing individual ECM and sensor/solenoid connector terminals with a digital voltmeter. See SCAN TESTER DATA table and SCAN TESTER USAGE .

Note. When using a scan tester, there is a time delay between serial data updates. For instantaneous response, a digital voltmeter must be used.

If scan tester is not available, MIL flashes can be read by grounding DLC terminal with ignition on and engine off. For example, FLASH, FLASH, pause, FLASH, longer pause, indicates Code 21. The first series of flashes are the first digit of trouble code. The second series of flashes are the second digit of trouble code. Trouble codes are displayed starting with the lowest code. Each code is displayed 3 times and will continue as long as DLC is grounded.

Note. Trouble codes will be recorded at various operating times. Some codes require sensor or switch operation for 5 seconds and others may require longer under certain conditions. Some codes may not set in a service bay operational mode.

TROUBLE CODE IDENTIFICATION

Note. Trouble code charts should only be used if Malfunction Indicator Light (MIL) is illuminated (indicating a current problem exists). Exceptions are Code 13, 15, 24, 44 and 45 charts, which may be used to help diagnose intermittent codes. Anytime Code 51, 52 or 55 is displayed with another code, start with 50-series code first and proceed to lower numbered codes.

HARD OR INTERMITTENT TROUBLE CODE DETERMINATION

During any diagnostic procedure, determine if codes are due to hard or intermittent failure. Diagnostic charts will not usually help diagnose intermittent codes. To determine hard codes and intermittent codes, proceed as follows

1. MANUALLY enter diagnostic mode. Read and record all stored trouble codes. Exit diagnostic mode and clear trouble codes. See «CLEARING TROUBLE CODES»(ref-19444-S17762370622001010200000) .
2. Apply parking brake and place transmission in Neutral or Park. Block drive wheels and start engine. MIL should go out. Run warm engine at specified curb idle for 2 minutes and note MIL.
3. If MIL comes on, manually enter diagnostic mode. Read and record trouble codes. This reveals hard failure codes. Codes 13, 15, 24, 44, 45 and 55 may require a road test to reset hard failure after trouble codes were cleared.
4. If MIL does not come on, all stored trouble codes were intermittent failures. Exceptions are noted under «DIAGNOSTIC PROCEDURE»(ref-19444-S27902347322001010200000) .

CLEARING TROUBLE CODES

Turn ignition switch to ON position and ground diagnostic test terminal "B" at DLC. see scheme 1 Turn ignition switch to OFF position and remove ECM fuse from fuse block for 10 seconds. Replace fuse. Remove diagnostic terminal ground lead. Codes may also be cleared using the General Motors Tech 1 scan tester.

Diagnostic Aids

Diagnostic aids (located in many trouble code charts) are provided as additional tips to help with diagnosis when inspected circuit is okay.

SPECIAL TOOLS (DIAGNOSTIC)

Note. A special scan tester, plugged into the DLC, can read trouble codes, check system voltages on the serial data line and save a great deal of time. For additional information, see tester owner's manual. Also, see SCAN TESTER USAGE and SCAN TESTER DATA .

The computerized engine control system is most easily diagnosed using a scan tester. However, other tools may aid in diagnosing problems if a scan tester is unavailable. These tools are a tachometer, test light, ohmmeter, digital voltmeter with 10-megohm input impedance (minimum), vacuum pump, vacuum gauge, fuel injector test lights and 6 jumper wires 6" long (one wire with female connectors at both ends, one wire with male connector at both ends and 4 wires with male and female connectors at opposite ends). A test light, rather than a voltmeter, must be used when indicated by a diagnostic chart.

SELF-DIAGNOSTIC TESTS

Note. The following diagnostic flow charts and mini-schematics are supplied courtesy of General Motors Corp.

Verify a clean, tight connection for ground circuit No. 413. An open circuit at sensor signal terminal or ground terminal will result in a Code 13.

CODE 13 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION

CODE 13, Schematic, Oxygen Sensor Circuit. Scheme 215

CODE 13, Flowchart, Oxygen Sensor Circuit. Scheme 216

After engine is started, temperature should rise steadily to about 194°F (90°C), then stabilize when thermostat opens. If engine is allowed to cool overnight, coolant temperature sensor and MAT sensor (if equipped) should read close to each other, when measured with a scan tester.

CODE 14 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION

TEMPERATURE-TO-RESISTANCE VALUES (1) (2)

CODE 14, Schematic, Coolant Sensor Signal Voltage Low. Scheme 217

CODE 14, Flowchart, Coolant Sensor Signal Voltage Low. Scheme 218

After engine starts, temperature should rise steadily to about 194°F (90°C) and stabilize when thermostat opens. If engine is allowed to cool overnight, coolant temperature sensor and MAT sensor (if equipped) should read close to each other when measured with a scan tester. Code 15 will also set if sensor signal or ground circuit is open.

CODE 15 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION

TEMPERATURE-TO-RESISTANCE VALUES (1) (2)

CODE 15, Flowchart, Coolant Sensor Signal Voltage High. Scheme 219

Check for poor connections or damaged harness. Also, check for an intermittent condition by starting engine and wiggling connection while monitoring battery voltage on scan tester. If voltage status changes abruptly or engine stalls, check for loose connections.

Note. When Code 16 sets, transaxle will be forced to 3rd gear, preventing erratic shifting due to improper voltage.

CODE 16, Schematic, Signal Voltage High/Low 3.8L. Scheme 220

CODE 16, Flowchart, Signal Voltage High/Low 3.8L. Scheme 221

Check connections at VSS buffer and PCM. If other codes are set along with Code 16 refer to appropriate code chart for diagnosis and repair.

CODE 16, Schematic, Trans. Output Speed (4.3L S & T Series Util. W/ M/T; 4.3L W/ 4L60E Trans. Scheme 222

CODE 16, Flowchart, Trans. Output Speed (4.3L S & T Series Util. W/ M/T; 4.3L W/ 4L60E Trans. Scheme 223

An intermittent may be caused by a poor connection, rubbed-through wire insulation or a wire broken inside insulation. Also, check for backed-out connector terminals or broken insulation spark reference circuit. If everything checks okay, try wiggling related wiring harness and connectors while engine is idling. This may help to isolate location of malfunction.

CODE 17, Schematic, RPM Signal Problem 3.8L. Scheme 224

CODE 17, Flowchart, RPM Signal Problem 3.8L. Scheme 225

Code 18 indicates an intermittent fault and may not set immediately or under all conditions. Symptoms experienced may help isolate cause of condition. A poor connection or fault in any cam sensor circuit or a faulty cam sensor may cause PCM to re-initialize injector sequence, causing a possible stumble or miss. A poor connection or fault in any crank sensor circuit or fuel control circuit or bent or missing vanes on harmonic balancer interrupter rings will cause PCM to stop pulsing injectors when fault occurs. This will cause an intermittent stumble or stall.

CODE 18, Flowchart, Cam/Crank Sensor 3.8L. Scheme 226

A scan tester displays throttle position in volts. Closed throttle voltage should be less than 1.0 volt (4.3L Turbo) or less than 1.25 volts (all other models). TPS voltage should increase at a steady rate to about 4.5 volts as throttle angle increases. Code 21 will also result if ground circuit is open or TPS signal circuit is shorted to voltage.

CODE 21 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION

CODE 21, Schematic, TPS Signal Voltage High. Scheme 227

CODE 21, Flowchart, TPS Signal Voltage High. Scheme 228

A scan tester displays throttle position in volts. Closed throttle voltage should be less than 1.0 volt (4.3L Turbo) or less than 1.25 volts (all other models). TPS voltage should increase at a steady rate to about 4.5 volts as throttle angle increases. Code 22 will also set if TPS signal or ground circuits are open or grounded.

CODE 22 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION

CODE 22, Flowchart, TPS Signal Voltage Low. Scheme 229

If engine is allowed to cool overnight, coolant and MAT sensors should read close to each other, when measured with a scan tester. A Code 23 will also result if signal and ground circuits become open.

CODE 23 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION

TEMPERATURE-TO-RESISTANCE VALUES (1) (2)

CODE 23 - MAT Sensor Temp. Low Schematic (3.8L & 4.3L CPI). Scheme 230

CODE 23 - MAT Sensor Temp. Low Flowchart (3.8L & 4.3L CPI). Scheme 231

Scan tester reading should closely match speedometer reading with drive wheels turning. If vehicle is equipped with an automatic transmission, check park/neutral switch adjustment. If no problem is found while using flow chart, see INTERMITTENTS in TESTS W/O CODES article in this section.

CODE 24, Schematic, VSS (4.3L C, K & P Series W/ M/T). Scheme 232

CODE 24, Schematic, VSS (4.3L Turbo). Scheme 233

CODE 24, Flowchart, Vehicle Speed Sensor (VSS). Scheme 234

A faulty or misadjusted Park/Neutral switch may set a false Code 24. Use scan tester and check for proper signal in Drive, while wiggling shifter. Scan tester MPH reading should closely match speedometer when vehicle is moving. If code is intermittent, see INTERMITTENTS in TESTS W/O CODES article in this section.

CODE 24, Schematic, VSS (3.1L). Scheme 235

CODE 24 - Flowchart, VSS (3.1L). Scheme 236

A faulty or misadjusted park/neutral switch may set a false Code 24. Use scan tester to check for proper signal in Drive while wiggling shifter. Code 24 may set if vehicle is power braked (brakes applied and throttle depressed) for more than 10 seconds. Check circuits No. 400 and 401 for proper connections.

CODE 24, Schematic, VSS (3.8L). Scheme 237

CODE 24, Flowchart, VSS (3.8L). Scheme 238

Check all connections, especially those at transmission pass-through connector. If code is intermittent, see INTERMITTENTS in TESTS W/O CODES article in this section. While Code 24 is set, scan tester will display an RPM derived from input speed. If input speed sensor is not operational at start-up, this can cause VSS to read zero.

CODE 24, Schematic, VSS (4.3L S & T Series P/U W/ M/T Exc. Turbo). Scheme 239

CODE 24, Schematic, VSS (4WD W/ 4L80E Transmission). Scheme 240

CODE 24, Flowchart, VSS (4.3L S & T W/ M/T & 4WD W/ 4L80E Trans.). Scheme 241

Check all connections, especially those at transmission pass-through connector. If code is intermittent, see INTERMITTENTS in TESTS W/O CODES article in this section. While Code 24 is set, scan tester will display an RPM derived from input speed.

CODE 24, Schematic, VSS (2WD W/ 4L80E Transmission). Scheme 242

CODE 24, Flowchart, VSS (4.3L S & T Utility W/ M/T; 4.3L W/4L60E Trans. & 2WD W/ 4L80E Trans.). Scheme 243

If engine is allowed to cool overnight, coolant temperature sensor and MAT sensor should read close to each other, when measured with a scan tester. A Code 25 will also result if sensor signal circuit is shorted to ground.

CODE 25 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION

TEMPERATURE-TO-RESISTANCE VALUES (1) (2)

CODE 25, Flowchart, MAT Sensor Temp. High (3.8L & 4.3L CPI). Scheme 244

QDM Symptoms

1. Puller fan on all the time or will not come on at all.
2. TCC does not engage.
3. Poor driveability due to 100 percent canister purge.

Monitor voltage of each terminal while moving related harness connectors, including PCM harness. If fault is induced, voltage will change. This may help locate intermittent problems. If code reappears with no apparent problems, replace PCM.

CODE 26, Schematic, Quad Driver Circuit (3.8L). Scheme 245

CODE 26, Flowchart, Quad Driver Circuit (3.8L)(1 of 2). Scheme 246

Intermittent faults must be continuously present for 200 milliseconds to cause Code 26 to set. QDM-controlled circuits should be inspected for poor terminal contact or damaged harnesses. QDM faults can be detected when outputs are on or off as follows

1. Open circuit or control circuit shorted to ground - output commanded off.
2. Shorted device or control circuit shorted to voltage - output commanded on.

CODE 26, Schematic, Quad Driver No. 1 (4.3L S & T P/U W/M/T). Scheme 247

CODE 26, Flowchart, Quad Driver No. 1 (4.3L S & T P/U W/M/T). Scheme 248

Intermittent faults must be continuously present for 200 milliseconds to cause Code 26 to set. QDM-controlled circuits should be inspected for poor terminal contact or damaged harnesses. QDM faults can be detected when outputs are on or off as follows

1. Open circuit or control circuit shorted to ground - output commanded off.
2. Shorted device or control circuit shorted to voltage - output commanded on.

CODE 27, Schematic, Quad Driver No. 2 (4.3L S & T P/U W/M/T). Scheme 249

CODE 27, Flowchart, Quad Driver No. 2 (4.3L S & T P/U W/M/T). Scheme 250

Check for poor connections or damaged harness. Monitor scan tester status for gear selector switch while wiggling harness.

CODE 31, Schematic, Park/Neutral Switch Circuit (3.8L). Scheme 251

CODE 31, Flowchart, Park/Neutral Switch Circuit (3.8L). Scheme 252

The EGR system may become inoperative if the park/neutral switch is out of adjustment.

Prior to replacing PCM, check resistance of all PCM-controlled solenoids and relays. Replace any with a resistance value less than 20 ohms.

CODE 32, Schematic, EGR System Error (4.3L G Series & 4.3L C,K, & M Series; All Non-Cal. W/ 4L60E Trans. Exc. 4.3L CPI). Scheme 253

CODE 32, Schematic, EGR System Error (4.3L C, G, K & P Series W/ 4L80E Trans.). Scheme 254

CODE 32, Flowchart, EGR System Error (4.3L G Series; 4.3L C,K & M Series (All Non-Cal.) & 4.3L C,G,K & P Series W/ 4L80E Trans.). Scheme 255

Prior to replacing PCM, check resistance of all PCM-controlled solenoids and relays. Replace any with a resistance value less than 20 ohms.

CODE 32, Schematic, EGR System Error (4.3L S & T Series Util. W/ M/T (Exc. CPI)). Scheme 256

CODE 32, Flowchart, EGR System Error (4.3L S & T Series Util. W/ M/T (Exc. CPI)). Scheme 257

Prior to replacing PCM, check resistance of all PCM-controlled solenoids and relays. Replace any solenoids or relays with a resistance value less than 20 ohms.

CODE 32, Schematic, EGR System Error (4.3L C & K Series & 4.3L P Series). Scheme 258

CODE 32, Schematic, EGR System Error (4.3L S & T Series P/U- Exc. Turbo & CPI). Scheme 259

CODE 32, Flowchart, EGR System Error (4.3L C,K & P Series & 4.3L S & T Series (Exc. Turbo & CPI)). Scheme 260

Vacuum switch in EGR solenoid is not used. If EGR valve sticks open, a rough idle will result. If EGR solenoid vent filter becomes plugged, EGR valve will remain open or close slowly. An inoperative check valve in ported vacuum supply line will result in faulty EGR system operation.

CODE 32, Schematic, EGR System Error (4.3L Turbo). Scheme 261

CODE 32, Flowchart, EGR System Error (4.3L Turbo). Scheme 262

Before replacing ECM, use an ohmmeter and check EGR valve resistances. Resistance between terminals "A" and "E" should be 9.5-10.5 ohms. Resistance between terminals "B" and "D" should be greater than 3000 ohms. Resistance between terminals "B" and "C" should start at 700 ohms and increase to about 4000 ohms as pintle is slowly moved inward.

CODE 32, Schematic, Linear EGR System Error (4.3L S & T Series W/ CPI). Scheme 263

CODE 32, Schematic, Linear EGR System Error (4.3L C & M Series (Cal.) & 4.3L L & M Series W/ CPI). Scheme 264

CODE 32, Flowchart, EGR System Error (4.3L W/ Linear EGR). Scheme 265

With ignition switch in ON position and engine off, manifold pressure is equal to atmospheric pressure and signal voltage is high. Comparing BARO readings from a known good vehicle using the same sensor is a good way to check accuracy of suspected sensor. Readings should be within .4 volt of each other. Code 33 will also result if ground circuit is open or MAP signal circuit is shorted to voltage or to 5-volt reference circuit.

CODE 33 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION

CODE 33, Schematic, MAP Sensor Signal Voltage High. Scheme 266

CODE 33, Flowchart, MAP Sensor Signal Voltage High. Scheme 267

With ignition switch in ON position and engine off, manifold pressure is equal to atmospheric pressure and signal voltage will be high. Comparing BARO readings with a known good vehicle using the same sensor is a good way to check accuracy of suspected sensor. Readings should be within .4 volt of each other. A Code 34 will also result if 5-volt reference and MAP signal circuits are open or shorted to ground. If 5-volt reference circuit is not shorted to ground and a Code 22 is stored, check MAP signal circuit for short to ground.

CODE 34 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION

CODE 34, Flowchart, MAP Sensor Signal Voltage Low (Exc. 3.8L). Scheme 268

MAF sensor produces a frequency signal, which cannot be easily measured. Check for following

1. Poor Connections - Inspect control module MAF signal pins and harness connectors for backed-out terminals, improper connector mating, broken locks, improperly formed or damaged terminals and poor terminal-to-wire connection.
2. Harness - Inspect MAF sensor harness to ensure it is not too close to high voltage wires, such as spark plug wires.
3. Intermittents - If harness appears okay, use scan tester to check MAF while moving related connectors and wiring harness. A change in display would indicate intermittent fault location.

CODE 34, Schematic, MAP Sensor Signal Voltage Low (3.8L). Scheme 269

CODE 34, Flowchart, MAP Sensor Signal Voltage Low (3.8L). Scheme 270

A slow, unstable idle may be caused by a system problem that cannot be overcome by IAC. Scan counts will be greater than 60 if too low, and zero counts if too high. If idle is too high, stop engine. With ignition on, ground ALDL test terminal "B". Wait 45 seconds for IAC to seat, then disconnect IAC. Start engine. If idle speed is greater than 800 RPM, inspect vehicle for vacuum leaks.

When Code 36 is set, transaxle will be forced into 3rd gear. If code sets due to a grounded circuit No. 1223, only 1st and 2nd gear operation will be available. If circuit No. 1223 is open, only 3rd and 4th gear operation will be available. If fault goes away, normal operation will be resumed for duration of key cycle.

CODE 36, Schematic, Shift Control Problem (3.8L). Scheme 271

CODE 36, Flowchart, Shift Control Problem(3.8L Chev. & Olds.). Scheme 272

CODE 36, Flowchart, Shift Control Problem (3.8L Pontiac). Scheme 273

A Code 38 in conjunction with a Code 26 would mean a problem with one or more of following components

1. Fuse or power supply circuit, brake switch or wire before splice.
2. Code 38 alone is result of a wire or circuit problem between splice and control module, poor connection to control module, or possibly control module itself.

If brake switch has failed in an open state, TCC will not engage. When code is set TCC will not engage and PCM will not allow 4th gear. Code 38 does not turn on SERVICE ENGINE SOON light on all models.

CODE 38, Schematic, Brake Switch Circuit (3.8L). Scheme 274

CODE 38, Flowchart, Brake Switch Circuit (3.8L). Scheme 275

Check circuit for potential open. Also, check for proper installation of PROM (MEM-CAL).

CODE 38, Schematic, Knock Sensor Circuit Open (4.3L S & T Series P/U W/ M/T). Scheme 276

CODE 38, Flowchart, Knock Sensor Circuit Open (4.3L S & T Series P/U W/ M/T). Scheme 277

Scan tester only indicates when PCM has commanded TCC on. This does not indicate TCC is actually engaged. To determine if TCC is engaging, road test vehicle. Engine RPM should decrease when scan tester indicates TCC engagement.

CODE 39, Flowchart, TCC Circuit (3.8L). Scheme 278

Check circuit for potential short to ground. Also, check for proper installation of PROM (MEM-CAL).

CODE 39, Flowchart, Knock Sensor Circuit Shorted (4.3L S & T Series W/ M/T). Scheme 279

An intermittent may be caused by a poor connection, rubbed-through wire insulation or a wire broken inside insulation. Check for following

1. Poor Connection - Inspect ECM harness connectors for backed-out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection and damaged harness.
2. Intermittents - If connections and harness are okay, connect a digital volt-ohmmeter (10-megohm) between ECM CAM signal circuit terminal and ground. Monitor DVOM while moving related connectors and wiring harness. Voltage reading will change if failure is induced. This may help isolate malfunction.

CODE 41, Flowchart, Cam Sensor Circuit (3.8L). Scheme 280

The scan tester cannot help diagnose a Code 42 problem. See INTERMITTENTS in TESTS W/O CODES article in this section.

CODE 42, Schematic, Elec. Spark Timing (4.3L C, K & P Series W/ M/T). Scheme 281

CODE 42, Schematic, Elec. Spark Timing (3.1L). Scheme 282

CODE 42, Schematic, Elec. Spark Timing (4.3L Turbo). Scheme 283

CODE 42, Schematic, Elec. Spark Timing (4.3L S & T Series P/U W/ M/T). Scheme 284

CODE 42, Schematic, Elec. Spark Timing (4.3L S & T Series Util. W/ M/T & All Models W/ 4L60E Trans. (Exc. CPI)). Scheme 285

CODE 42, Schematic, Elec. Spark Timing (W/ 4L60E Trans & CPI). Scheme 286

CODE 42, Schematic, Elec. Spark Timing (All W/ 4L80E Trans.). Scheme 287

CODE 42, Flowchart, Elec. Spark Timing (Exc. 3.8L). Scheme 288

An intermittent may be caused by a poor connection, rubbed-through wire insulation or a wire broken inside insulation. Inspect ECM harness connectors for backed-out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection and damaged harness.

If connections and harness are okay, connect a digital volt-ohmmeter between affected terminal to ground, and monitor meter while moving related connectors and wiring harness. If failure is induced, voltage reading will change.

CODE 42, Flowchart, Elec. Spark Timing (3.8L). Scheme 289

Code 43 can be caused by a faulty knock sensor connection at ESC module or ECM. Also, check controller-to-ECM signal line for an open or short to ground.

CODE 43, Schematic, ESC W/ Spark Control Module (3.1L). Scheme 290

CODE 43, Schematic, ESC W/ Spark Control Module (Exc. 3.1L). Scheme 291

CODE 43, Flowchart, ESC W/ Spark Control Module. Scheme 292

ECM/PCM applies and monitors a 5-volt DC signal to knock sensor. Internal knock sensor circuitry pulls this DC signal down to about 2.5 volts. When knock sensor detects detonation, it generates an AC signal which rides back on DC signal to ECM/PCM. Knock signal intensity is dependent upon knock signal level.

CODE 43, Schematic, ESC W/O Module (Exc. 4.3L S & T Series P/U W/ M/T & 4/3L CPI). Scheme 293

CODE 43, Flowchart, ESC W/O Module (Exc. 4.3L S & T Series P/U W/ M/T & 4.3L CPI). Scheme 294

VCM applies and monitors a 5-volt DC signal to knock sensors. Internal knock sensor circuitry pulls this DC signal down to about 2.5 volts. When knock sensor detects detonation, it generates an AC signal which rides back on DC signal to VCM. Knock signal intensity is dependent upon knock signal level.

CODE 43, Schematic, ESC (4.3L S & T Series W/ M/T & L & M Series W/ 4.3L CPI). Scheme 295

CODE 43, Flowchart, ESC (4.3L S & T Series W/ M/T & L & M Series W/ 4.3L CPI). Scheme 296

Using scan tester, observe Block Learn Memory (BLM) value at different RPMs. If Code 44 conditions exist, block learn value will be around 150-172.

Using scan tester, observe Block Learn Memory (BLM) value at different RPMs. If Code 44 conditions exist, block learn value will be around 150.

Code 45, rich exhaust, is most likely caused by one of the following

Code 45, rich exhaust, is most likely caused by one of the following

Check for poor harness connections or harness damage. If no problems are found, turn ignition on. Backprobe applicable PCM terminals with a DVOM while wiggling harness. If a failure is induced, voltage reading will change. If no problems are found, check EGR valve pintles and orifices for excessive carbon build-up. Also, check for plugged EGR tube or passages.

CODE 53-55, Schematic, EGR Fault (3.8L). Scheme 297

CODE 53-55, Flowchart, EGR Fault (3.8L). Scheme 298

QUAD-DRIVER RELATED SYMPTOMS

1. Improper shifting.
2. TCC will not apply or harsh engagement.
3. Poor driveability due to constant EGR.

Monitor voltage at each terminal shown in schematic while moving related harness connectors, including PCM harness. If failure is induced, voltage will change. This may help to isolate an intermittent condition. Check for bent pins at PCM. If code reoccurs with no apparent connection problem, replace PCM.

CODE 56, Schematic, Quad Driver "B" Fault (3.8L). Scheme 299

CODE 56, Flowchart, Quad Driver "B" Fault (3.8L)(1 of 2). Scheme 300

CODE 56, Flowchart, Quad Driver "B" Fault (3.8L)(2 of 2). Scheme 301

An intermittently binding or sticking throttle cable cam cause a Code 68 to set. Code can also be set by manually compressing servo to increase engine RPM. Outside interference such as CB antenna lead near PCM wiring harness may cause false servo position sensor signal and set Code 68.

CODE 68, Flowchart, Cruise System Prob. Using Tech-1 (3.8L). Scheme 302