Engine Controls - Tests W/codes - V8: Diagnosis Chevrolet Pickup K1500

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-91383-S25663593002001031200000) . 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 I - SYS/COMP 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-91383-S07121270022001031200000) .
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-91383-S39110146752001031200000) .

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.

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, Open Oxygen Sensor Circuit. Scheme 339

CODE 13, Flowchart, Open Oxygen Sensor Circuit. Scheme 340

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 341

CODE 14, Flowchart, Coolant Sensor Signal Voltage Low. Scheme 342

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 343

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 (5.0L & 5.7L W/ 4L60E Trans.). Scheme 344

CODE 16, Flowchart, Trans. Output Speed (5.0L & 5.7L W/ 4L60E Trans.). Scheme 345

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 346

CODE 21, Flowchart, TPS Signal Voltage High. Scheme 347

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 348

DTC 24, VEHICLE SPEED SIGNAL LOW ("C" & "K" SERIES, M/T ONLY)

The ECM applies and monitors 12 volts on circuit No. 437. Circuit No. 437 connects to Vehicle Speed Sensor (VSS) buffer, which alternately grounds circuit No. 437 when receiving voltage pulses from VSS (drive wheels are turning). The pulsing action occurs approximately 2000 times per mile and the ECM calculates vehicle speed based on the time between pulses. Scan tester reading should closely match speedometer reading with drive wheels turning.

Note. Test numbers refer to numbers on diagnostic chart.

1. DTC 24 will set after the following conditions are met for at least 40 seconds: circuit No. 437 voltage is constant, engine speed is more than 2000 RPM, and vehicle speed signal at ECM terminal A9 is less than 5 MPH.
2. This test determines if VSS buffer is receiving alternating current signal from vehicle speed sensor. Use Digital Volt-Ohmmeter (DVOM) on 20-volt AC scale.
3. This test monitors voltage on circuit No. 437. With wheels turning, the pulsating action causes a varying voltage. Voltage variation will be greater at low wheel speeds and an average of 4-6 volts at about 20 MPH.

With drive wheels turning, scan tester and speedometer reading should closely match.

Scheme 349

Scheme 350

DTC 24, VEHICLE SPEED SIGNAL LOW (WITH 4L60-E A/T)

The speed sensor circuit consists of a magnetic-induction sensor, Vehicle Speed Sensor (VSS) buffer, and wiring. Gear teeth on output shaft induce an alternating current in sensor. This signal is then transmitted to buffer. The buffer compensates for various axle ratios and converts signal into a square wave signal for use by the speedometer, cruise control ABS, and ECM.

The buffer sends 2 different signals to the ECM. circuit No. 437 relays transmission output speed, which is used to control shift points, line pressure torque converter clutch and DTC 24 and 72. Circuit No. 1716 relays vehicle speed which is used to control engine operating conditions and DTC 16. When DTC 24 sets, only 2nd gear at maximum line pressure will occur. DTC 24 sets when the following conditions are met for 6.4 seconds

1. Transmission is not in Park or Neutral.
2. Circuit No. 437 voltage is constant.
3. Engine speed is more than 3000 RPM.
4. Output speed less than 250 RPM.
5. Manifold absolute pressure 14.5-36.9 psi (100-255 kPa).
6. Throttle position 10-100 percent. NOTE: Test numbers refer to numbers on diagnostic chart.

1. This test monitors voltage on circuit No. 437. With wheels turning, the pulsating action causes a varying voltage. Voltage variation will be greater at low wheel speeds and an average of 4-6 volts at about 20 MPH.
2. Less than one volt at ECM connector indicates circuit No. 437 is shorted to ground. Disconnect circuit No. 437 at VSS buffer. If voltage now reads more than 10 volts, the VSS buffer is faulty. If voltage remains less than 10 volts, then circuit No. 437 is grounded. If circuit No. 437 is not grounded, check for a faulty ECM connector or ECM.
3. A steady 8-12 volt reading at the ECM connector indicates that circuit No. 437 is open or VSS buffer is faulty.

Check all connections at transmission pass-through connector.

Scheme 351

Scheme 352

DTC 24, VEHICLE SPEED SIGNAL LOW (WITH 4L80-E A/T)

The PCM/TCM applies and monitors 12 volts on circuit No. 437. Circuit No. 437 connects to Vehicle Speed Sensor (VSS) buffer, which alternately grounds circuit No. 437 when receiving voltage pulses from VSS (drive wheels are turning). The pulsing action occurs approximately 2000 times per mile and the ECM calculates vehicle speed based on the time between pulses. Scan tester reading should closely match speedometer reading with drive wheels turning. DTC 24 sets when the following conditions are met for 5 seconds

1. Transmission is not in Park or Neutral.
2. Circuit No. 437 voltage is constant.
3. Engine speed is more than 1200 RPM.
4. VSS signal indicates less than 2 MPH. NOTE: Test numbers refer to numbers on diagnostic chart.

1. This test monitors voltage on circuit No. 437. With wheels turning, the pulsating action causes a varying voltage. Voltage variation will be greater at low wheel speeds and an average of 4-6 volts at about 20 MPH.
2. Less than one volt at PCM/TCM connector indicates circuit No. 437 is shorted to ground. Disconnect circuit No. 437 at VSS buffer. If voltage now reads more than 10 volts, the VSS buffer is faulty. If voltage remains less than 10 volts, then circuit No. 437 is grounded. If circuit No. 437 is not grounded, check for a faulty PCM/TCM connector or faulty PCM/TCM.
3. A steady 8-12 volt reading at the PCM/TCM connector indicates circuit No. 437 is open or VSS buffer is faulty.
4. This is normal voltage, which indicates a possible intermittent condition.

Check all connections at transmission pass-through connector.

Scheme 353

Scheme 354

Before replacing PCM, use ohmmeter to check resistance of each PCM-controlled relay and solenoid. Replace any relay or solenoid where resistance is less than 20 ohms.

CODE 31, Schematic, Engine Speed Governor (5.7L "G" Series). Scheme 355

CODE 31, Flowchart, Engine Speed Governor (5.7L "G" Series). Scheme 356

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 (5.0L & 5.7L "G" Series, Non-Cal. W/ 4L60E Trans). Scheme 357

CODE 32, Flowchart, EGR System Error (5.0L & 5.7L "G" Series). Scheme 358

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 Sys. Error (5.0L & 5.7L C & K Series Cal. W/ 4L60E Trans.). Scheme 359

CODE 32, Schematic, EGR Sys. Error (5.7L & 7.4L C,G,K & P Series W/ 4L80E Trans). Scheme 360

CODE 32, Flowchart, EGR Sys. Error (5.0L & 5.7L C & K Series W/ 4L60E Trans; 5.7L & 7.4L C,G,K & P Series W/ 4L80E Trans.). Scheme 361

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 Sys. Error (5.0L & 5.7L C & K Series W/ M/T). Scheme 362

CODE 32, Schematic, EGR Sys. Error (5.7L P Series & 7.4L C & K Series W/ M/T). Scheme 363

CODE 32, Flowchart, EGR Sys. Error (5.0L & 5.7L C & K Series; 5.7L P Series; 7.4L C & K Series; All W/ M/T). Scheme 364

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 Voltage High. Scheme 365

CODE 33, Flowchart, MAP Sensor Voltage High. Scheme 366

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. Scheme 367

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.

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 (V8 C, K & P Series W/ M/T). Scheme 368

CODE 42, Schematic, Elec. Spark Timing (All Models W/ 4L60E Trans. Exc. CPI). Scheme 369

CODE 42, Schematic, Elec. Spark Timing (All W/ 4L60E Trans. & CPI). Scheme 370

CODE 42, Schematic, Elec. Spark Timing (All W/ 4L80E Trans.). Scheme 371

CODE 42, Flowchart, Elec. Spark Timing. Scheme 372

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 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION

CODE 43, Schematic, ESC W/ Spark Control Module. Scheme 373

CODE 43, Flowchart, ESC W/ Spark Control Module. Scheme 374

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 Spark Control Module. Scheme 375

CODE 43, Flowchart, ESC W/O Spark Control Module. Scheme 376

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.

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