Engine Controls - Basic Testing: Diagnosis Chevrolet Pickup C1500

VISUAL INSPECTION

Visually inspect all electrical wiring. Look for chafed, stretched, cut or pinched wiring. Ensure electrical connectors fit tightly and are not corroded. Ensure vacuum hoses are properly routed and not pinched or cut. If necessary, see VACUUM DIAGRAMS article in this section to verify routing and connections. Inspect air induction system for possible vacuum leaks.

A-3, NO-START DIAGNOSIS

Note. For diesel information, see TESTS W/CODES - DIESEL and TESTS W/O CODES articles in the ENGINE PERFORMANCE Section.

Diagnostic Aids

If no trouble is found in fule pump circuit or ignition system and cause of a "Engine Cranks But Will Not Run" condition has not been found, check for

1. Fouled spark plugs.
2. EGR valve stuck open.
3. Low fuel pressure. See BASIC FUEL SYSTEM CHECKS.
4. Water or foreign material in fuel system.
5. A ground circuit 423 (IC) may cause a "No Start" or a "Start Then Stall" condition.
6. Basic engine problem.

General Inspection

1. Ensure proper starting procedure is being used.
2. Visually check vacuum hoses for splits, kinks and improper connections. See underhood emission control information label. Check ignition wires for cracks, hardness and improper connections at distributor cap and spark plugs.
3. Remove spark plugs. Check and replace if necessary.
4. Remove distributor cap and check for moisture, dust, cracks, burns, and arcing to ground through coil mounting screws or rotor.
5. Try to turn distributor shaft by hand. Drive gear pin may be broken.
6. If vehicle has been exposed to very cold temperatures, ensure oil is of proper viscosity and not contaminated with gasoline.

1. Ensure proper starting procedure is being used. Visually check vacuum hoses for splits, kinks and proper connections as shown on Vehicle Emission Control Information (VECI) label. Check ignition wires for cracks, hardness and proper connections at both coil pack and spark plugs.
2. Remove spark plugs. Check and replace as necessary. In very cold temperatures, ensure oil is of proper viscosity and not contaminated with gasoline.

Scheme 3

1. Ensure Throttle Position (TP) sensor scans less than 2.5 volts. If not, see Code 21 chart in appropriate TESTS W/CODES article in this section. Check for stored trouble codes. See appropriate TESTS W/CODES article in this section. If engine has not been started for at least 8 hours, Intake Air Temperature (IAT) sensor scanned temperature should be close to CTS scanned temperature. Disconnect cam sensor and attempt to start engine. If engine starts, see Code 41 chart in appropriate TESTS W/CODES article in this section.
2. Reconnect cam sensor connector. Compare scanned CTS temperature with actual coolant temperature. If they are not close, replace coolant sensor. Depress accelerator pedal approximately 25 percent. Attempt to start engine. If engine does not start, go to next step. If engine starts, check IAC counts on scan tester. Check for stored Code 35. Check for blocked IAC passages.
3. Disconnect all injector connectors. Install injector test light in each injector harness connector. All lights should be off. Lights should blink as engine is cranked. If any injector lights are on, go to step 6). If lights do not blink at all while engine is cranked, go to step 7). If all lights are off and blink as engine is cranked, check for adequate spark using Spark Tester (ST-125). Check for spark on plug wires No. 1, 3 and 5 (one at a time). Leave matching plug wire connected while checking for spark. If spark jumps tester on all plug wires, check for faulty spark plugs or fuel system as cause of no-start condition. See A-7, BASIC FUEL SYSTEM CHECKS (GASOLINE). If spark is not present on any plug wire, ignition module connection is poor or ignition module is faulty.
4. If spark does not jump tester on all plug wires, ensure plug wire resistance is less than 30,000 ohms. Ensure ignition coil secondary resistance is 5000-6500 ohms at room temperature. Replace as necessary. If wires and coils are okay, remove coil that did not fire. Verify primary resistance of.3-.5 ohm. Replace coil if necessary. If coil is okay, connect a test light across ignition module terminals for problem coil.
5. Crank engine. If test light flashes, check for poor coil-to-module connections. If connections are okay, replace faulty coil. If test light does not flash, replace ignition module.
6. Turn ignition off. Disconnect PCM Black C-D connector. Turn ignition on. If all lights are now off, replace PCM. If any lights are still on, repair short to ground in that injector drive circuit.
7. Check ignition module power supply (20-amp INJ fuse and circuit). Repair as necessary. Disconnect fuel injector connector. Turn ignition on. With a test light connected to ground, check for battery voltage on Pink/Black wire of injector harness. If test light is on, go to next step. If test light is off, check injector harness between injector connectors and 20-amp INJ fuse. If fuse is blown, repair short to ground and replace fuse. If fuse is okay, check power supply to fuse and circuit between fuse and injector harness connector.
8. Turn ignition off. Disconnect ignition module connector. Turn ignition on. Install injector test light in any injector harness connector. Connect test light to battery voltage, and repeatedly touch terminal "D" of ignition module harness connector. (Scheme 3) Injector test light should flash each time test light touches terminal "D". If injector test light flashes, go to step 10).
9. If injector test light does not flash, check injector drive circuit between PCM and injector harness connector for open or short to voltage. Repair as necessary. If injector drive circuit is okay, check for open, short to ground or short to voltage on fuel control circuit No. 430. If circuit is okay, problem is faulty connection at PCM fuel control terminal or faulty PCM.
10. Turn ignition off. Using proper jumper adapter from Adapter Kit (J 35616), connect a fused jumper between ignition module harness connector terminal "N" and battery voltage. Connect a second jumper between ignition module harness connector terminal "M" and ground. Connect DVOM between ignition module harness connector terminal "H" and battery voltage. Observe voltmeter while cranking engine. Voltmeter should read approximately 1.7 volts.
11. If voltage is high, check circuit No. 646 for open or short to ground. If open or short to ground is not present, replace faulty crank sensor. If voltage is low, check circuit No. 646 for open or short to voltage. Check circuit No. 645 for open and circuit No. 644 for open or short to ground. If all circuits are okay, replace faulty crank sensor.
12. If voltage is approximately 1.7 volts, move DVOM lead from terminal "H" to terminal "G". Crank engine and monitor voltage. Voltmeter should read about 5.5 volts. If voltage is correct, go to next step. If voltage is less than 5.5 volts, check for open or short to voltage in circuit No. 643. If voltage is greater than 5.5 volts, check for short to ground in circuit No. 643. If no problem is found, crank sensor is faulty.
13. Turn ignition on. Probe ignition module harness connector terminal "P" with a DVOM connected to ground. If battery voltage is not present, repair open in ignition module power supply circuit. If battery voltage is present, problem is poor ignition module connections or faulty ignition module.

FUEL SYSTEM PRESSURE TEST

FUEL PUMP FLOW TEST

1. Disconnect fuel line at fuel filter inlet. Disconnect fuel injection pump electric shut-off solenoid wire (Pink).
2. Crank engine 15 seconds. If fuel pump does not supply approximately 1/2 pint of fuel in 15 seconds, go to appropriate FUEL SYSTEM PRESSURE TEST.

1. Turn engine off. Disconnect fuel line at inlet to fuel filter assembly. Install low pressure fuel gauge to fuel line.
2. Crank or run engine 10-15 seconds. If fuel pressure is not 5.8-8.7 psi (.41-.61 KG/cm 2 ), check fuel lines and fuel tank sending unit for restriction. If fuel lines and sending unit are okay, replace fuel pump.

DIAGNOSTIC CIRCUIT CHECK (GASOLINE)

There are different/unique types of control modules, and various systems are used to control their operation depending on engine and/or vehicle type. For easier referencing, engines and models are identified or divided into system groups. See SYSTEM GROUPING CHART .

SYSTEM GROUPING CHART

Diagnostic circuit check determines following

1. Whether Malfunction Indicator Light (MIL) works.
2. Whether ECM is operating and can recognize a fault.
3. Whether any codes are stored.

After performing basic diagnostic procedures listed under PRELIMINARY INSPECTION & ADJUSTMENTS; A-7, BASIC FUEL SYSTEM CHECKS (GASOLINE) and C-4, BASIC IGNITION SYSTEM CHECKS (GASOLINE), use self-diagnostic system for determining computer-related problems. (Scheme 14)

If codes are NOT indicated and driveability problems still exist after performing necessary tests in diagnostic circuit check, see TESTS W/O CODES article in this section and SCAN TESTER USAGE under SELF-DIAGNOSTIC SYSTEM in appropriate TESTS W/CODES article in this section.

1. Check MIL operation. Turn ignition on with scan tester not connected, DLC terminal not grounded and engine not running. MIL should be on steadily. If light glows and stays on steadily, go to next step. If light does not glow, go to A-1, MALFUNCTION INDICATOR LIGHT (MIL) INOPERATIVE. If light flashes, go to step 3).
2. Ground DLC test terminal "B". MIL should flash Code 12, followed by any codes stored in ECM memory. If light goes from bright to dim or if light remains on and does not flash Code 12, see A-2, MALFUNCTION INDICATOR LIGHT (MIL) ALWAYS ON OR WON'T FLASH CODE 12.
3. Check for short to ground in diagnostic test terminal wire between DLC terminal "B" and ECM terminal. (Scheme 4)- (Scheme 11). If circuit is okay, replace ECM.

Scheme 4

Scheme 5

Scheme 6

Scheme 7

Scheme 8

Scheme 9

Scheme 10

Scheme 11

DIAGNOSTIC CIRCUIT CHECK (DIESEL)

Note. Diesel equipped vehicles with light duty emissions are equipped with a self-diagnostic system. For information on diagnostic system circuit check and retrieving codes, see TESTS W/CODES - DIESEL article in the ENGINE PERFORMANCE section.

Preliminary Inspection

1. Check all vacuum hoses for incorrect routing, restrictions, cuts and other damage. Inspect hoses beneath air cleaner assembly and other engine components.
2. Inspect all wires in engine compartment for correct and good connections. Also check wires for pinched or chaffed spots, as well as contact with sharp edges or exhaust manifolds. (Scheme 12)or (Scheme 13).
3. Perform preliminary inspection carefully and thoroughly. A thorough inspection can often identify cause of problem without further diagnosis.

Diagnostic Procedure

1. Ensure all engine systems not related to Diesel Electronic Control (DEC) system are operating properly. DO NOT proceed with testing unless all problems not related to DEC system have been repaired. DEC system diagnosis should always begin with DIAGNOSTIC SYSTEM CHECK chart under DIAGNOSTIC CHARTS in «TESTS W/CODES - DIESEL»(ref-19435) article in this section. Performing this check determines whether DEC system and ECM are working properly.
2. If trouble codes (other than Code 12) are displayed, determine whether codes are hard or intermittent trouble codes. A hard code remains until code-setting condition is repaired. Hard codes cause Malfunction Indicator Light (MIL) to come on.
3. An intermittent code does not reset itself and is not present when vehicle is repaired. An intermittent code is often caused by loose connections. MIL goes out 10 seconds after fault goes away.

Scheme 12

Scheme 13

Diagnostic Circuit Check & Work Flow (Diesel). Scheme 14