Engine Controls - Tests W/codes - 5.7L: Other Chevrolet Suburban C2500

TERMINOLOGY

Due to Federal government requirements, manufacturers may use names and acronyms for systems and components different than those used in previous years. The following table will help eliminate confusion when dealing with these components and systems. Only relevant components and systems whose names have changed from current General Motors Corp. terminology have been listed.

SAE TERMINOLOGY

Hard Failures

Most hard failures cause MIL to illuminate and remain on until the malfunction is repaired. If light comes on and remains on (light may flash) during vehicle operation, cause must be found using diagnostic (code) charts. If a sensor fails, control unit will use a substitute value in its calculations to continue engine operation. In this condition, vehicle is functional, but driveability can be poor.

Intermittent Failures

Intermittent failures may cause MIL to flicker or illuminate and go out about 10 seconds after the intermittent fault goes away. The corresponding trouble code, however, will be retained in control module memory. If related fault does not reoccur within 50 engine restarts, it will be erased from ECM memory. Intermittent failures may be caused by faulty sensor, connector or wiring. See INTERMITTENTS in TESTS W/O CODES - GASOLINE article.

RETRIEVING CODES (NON-SCAN)

Note. The Assembly Line Data Link (ALDL) connector may also be referred to as the Data Link Connector (DLC) in flow charts. This is the same connector.

1. Turn ignition on with engine off. Malfunction Indicator Light (MIL) should glow. Locate Data Link Connector (DLC), attached to control module wiring harness. Most DLCs are located under dash on driver's side of vehicle. For exact location of DLC, see appropriate COMPONENT LOCATIONS illustration in «SYSTEM/COMPONENT TESTS - 5.7L»(ref-20084) article. Insert jumper wire from terminal "B" (diagnostic test terminal) to terminal "A" (ground) of DLC (terminals No. 5 and 6 of 16-terminal connector). (Scheme 87) Turn ignition on. NOTE: Inserting jumper wire into test and ground terminals of DLC with engine running will cause fuel-injected vehicles to enter field service mode and codes will not flash. See FIELD SERVICE MODE in «BASIC TESTING - 5.7L»(ref-20098) article.
2. Malfunction Indicator Light (MIL) should flash codes. Each code is flashed 3 times. If codes DO NOT flash, perform DIAGNOSTIC CIRCUIT CHECK (GASOLINE) in «BASIC TESTING - 5.7L»(ref-20098) article. To exit diagnostic mode, turn ignition off and remove jumper wire from DLC.

Scheme 87

Scheme 88

Field Service Mode Check

Malfunction Indicator Light (MIL) indicates operational mode of engine if DLC is grounded while engine is running. Light response confirms proper fuel system operation and verifies closed loop operation. Clear codes and perform this test after any repair is completed. Field service mode check can be found by proceeding to FIELD SERVICE MODE CHECK in BASIC TESTING - 5.7L article.

SCAN TESTER USAGE

Note. Before connecting scan tester, check diagnostic system and ensure accurate information is received by scan tester. Perform DIAGNOSTIC CIRCUIT (GASOLINE) CHECK in BASIC TESTING - 5.7L article. If vehicle does not pass diagnostic circuit check, information received by scan tester may be invalid.

The scan tester is a specialized tester which can diagnose on-board computer control systems by providing access to circuit voltage information without crawling under dash or hood to backprobe sensors and connectors. scan testers reduce diagnostic time by furnishing input data (voltage signals) which can be compared to specification parameters. See SCAN TESTER DATA .

Scan testers also furnish information on output device (solenoids and motors) status. However, status parameters are only an indication output signals have been sent to devices by the control module. They do not indicate whether devices respond properly to that signal. This must be verified at output device using a voltmeter or test light.

Note. On models not using "P" series codes, Code 12 should always exist when DLC test terminal is grounded with key on and engine off, but it may not be indicated by all makes of scan tester.

If trouble codes are not present, a problem may still exist. Driveability-related problems with codes displayed occur about 20 percent of the time, while driveability problems without codes occur about 80 percent of the time. Out-of-calibration sensors WILL NOT set a trouble code, but WILL cause driveability problems. A scan tester is the easiest method of checking sensor specifications and other data parameters. Tester is also useful in finding intermittent wiring problems by wiggling wiring harnesses and connections (key on, engine off) while observing data parameters. See SCAN TESTER DATA .

Note. Information obtained by scan tester is only as accurate as the tester itself. If erroneous voltage signals are suspected, verify tester information using a digital voltmeter and wiring schematic. If non-existent codes are displayed, turn ignition off and remove tester. Turn ignition on and ground DLC test terminal. If same codes are not flashed by Malfunction Indicator Light (MIL) as were indicated by scan tester, tester cannot be used on vehicle and information obtained by it will not be guaranteed accurate. If tested vehicle does not provide for grounding diagnostic test terminal, verify tester accuracy by connecting it to a known good vehicle.

SCAN TESTER DATA

Note. Information contained in the following table is typical of readings taken on vehicle with engine idling, upper radiator hose hot, throttle closed, transmission in Park or Neutral, closed loop status achieved and all accessories off (except as noted in tables). Not all devices and systems are used on all models. For additional information, see tester owner's manual.

SCAN TESTER DATA

System Too Lean

If air/fuel ratio is too lean, idle speed may be either too high (check for vacuum leaks) or too low. Engine speed may vary and disconnecting IAC may not help. Scan tester and/or digital voltmeter (10 megohm) will read an oxygen sensor output less than 300 mv (.3 volt). Check for low fuel pressure or water in fuel.

System Too Rich

If air/fuel ratio is too rich, idle speed will be too low and scan tester counts will usually be greater than 80. The system may be obviously rich with Black smoke from tailpipe. Scan tester and/or voltmeter will read an oxygen sensor voltage signal fixed greater than 800 mv (.8 volt). Look for high fuel pressure or leaking/sticky injectors. Remove IAC and inspect bore for foreign material or evidence of IAC valve dragging bore. A silicone-contaminated oxygen sensor will produce lean air/fuel mixture. Oxygen sensor output would be fixed greater than 800 mv (.8 volt). This may also set Code 45.

Throttle Body

Remove IAC and inspect bore for evidence of IAC valve dragging.

IAC Valve Connections

Carefully inspect connections for looseness or corrosion.

PCV Valve

The wrong PCV valve may cause incorrect idle speed.

CODE 35 TERMINAL & CIRCUIT WIRING IDENTIFICATION

Code 35 Schematic (5.7L) Idle Speed Error. Scheme 89

Code 35 Flow Chart (5.7L) Idle Speed Error. Scheme 90

O2 Sensor Wire

Wire may be mispositioned and touching exhaust manifold. Check for ground between sensor and wire connector.

Fuel Contamination

Water, even small amounts, near in-tank fuel pump inlet can reach fuel injector, causing a lean exhaust and setting Code 44.

Fuel Pressure

System will be lean if fuel pressure is low. It may be necessary to monitor fuel pressure while driving vehicle. For fuel pressure checking procedure, see BASIC TESTING - 5.7L article.

Exhaust Leaks

If exhaust system has large leaks, exhaust system negative pressure pulses can cause outside air to be drawn into system and past O2 sensor. Vacuum or crankcase leaks can also cause a lean condition. If Code 44 is intermittent, proceed to the INTERMITTENTS in TESTS W/O CODES - GASOLINE article.

CODE 44 TERMINAL & CIRCUIT WIRING IDENTIFICATION

Code 44 Flow Chart (5.7L) Lean Exhaust Indication. Scheme 91

Fuel Pressure High

If fuel pressure is too high, air/fuel ratio will be rich. For fuel pressure checking procedure, see BASIC TESTING - 5.7L article. The control module can compensate for slight increases but if air/fuel ratio becomes too rich a Code 45 will be set.

Ignition Ground

If an open occurs at circuit No. 453, HEI induced electrical "noise" may result, causing simulated reference pulses picked up by control module on IC harness reference line. Additional pulses result in a higher than actual engine speed signal. The control module will increase injector pulse width ("on" time) to match increased RPM signal. Scan tester will show higher than actual RPM, which can help diagnose problem.

Fuel Canister

Charcoal canister fuel saturation will cause a rich air/fuel ratio. If full of fuel, check canister control and hoses.

MAP Sensor

If control module senses higher than normal manifold pressure (low vacuum) system can go rich. Disconnecting MAP sensor allows control module to substitute a fixed value for MAP sensor. If rich condition disappears, replace MAP sensor and continue testing.

TPS

An intermittent TPS output will cause system to operate rich due to a false indication of engine acceleration.

O2 Sensor Contamination

O2 sensor contamination, caused by silicone in certain fuels or use of improper RTV sealant, may cause a White-powdery coating to cover O2 sensor. The false high signal voltage produced (or low oxygen content sensed) is interpreted by control module as a rich mixture, causing control module to set Code 45.

EGR Problem

EGR valve sticking open at idle is usually accompanied by a rough idle and/or stalling. If Code 45 is intermittent, see INTERMITTENTS in TESTS W/O CODES - GASOLINE article.

CODE 45 TERMINAL & CIRCUIT WIRING IDENTIFICATION

Code 45 Flow Chart (5.7L) Rich Exhaust Indication. Scheme 92

DTC87: HIGH GEAR RATIO ERROR

Control module calculates ratio based on transmission input speed and output speed sensor readings. Control module compares known ratio to calculated ratio.

1. An out-of-calibration transmission range pressure switch could falsely indicate actual transmission range.
2. This test verifies proper ratio.

SUMMARY

If hard fault codes are not present and driveability symptoms or intermittent codes exist, proceed to TESTS W/O CODES - GASOLINE article for diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.), or intermittent diagnostic procedures.

Wiring Diagram ("C" & "K" Series Pickup, Sierra, Suburban, Tahoe & Yukon - 5.7L With A/T - 1 Of 3). Scheme 93

Wiring Diagram ("C" & "K" Series Pickup, Sierra, Suburban, Tahoe & Yukon - 5.7L With A/T - 2 Of 3). Scheme 94

Wiring Diagram ("C" & "K" Series Pickup, Sierra, Suburban, Tahoe & Yukon - 5.7L With A/T - 3 Of 3). Scheme 95

Wiring Diagram ("C" & "K" Series Pickup, Sierra, Tahoe & Yukon - 5.7L With M/T - 1 Of 2). Scheme 96

Wiring Diagram ("C" & "K" Series Pickup, Sierra, Tahoe & Yukon - 5.7L With M/T - 2 Of 2). Scheme 97

Wiring Diagram ("P" Series - 5.7L With M/T - 1 Of 2). Scheme 98

Wiring Diagram ("P" Series - 5.7L With M/T - 2 Of 2). Scheme 99

Wiring Diagram ("P" Series - Commercial Van/Motorhome - 5.7L With 4L80-E - 1 Of 3). Scheme 100

Wiring Diagram ("P" Series - Commercial & Motorhome - 5.7L With 4L80-E - 2 Of 3). Scheme 101

Wiring Diagram ("P" Series - Commercial & Motorhome - 5.7L With 4L80-E - 3 Of 3). Scheme 102

Wiring Diagram ("P" Series - Cutaway - 5.7L - 1 Of 3). Scheme 103

Wiring Diagram ("P" Series - Cutaway - 5.7L - 2 Of 3). Scheme 104

Wiring Diagram ("P" Series - Cutaway - 5.7L - 3 Of 3). Scheme 105

Wiring Diagram (Van - 5.7L With 4L60-E - 1 Of 3). Scheme 106

Wiring Diagram (Van - 5.7L With 4L60-E - 2 Of 3). Scheme 107

Wiring Diagram (Van - 5.7L With 4L60-E - 3 Of 3). Scheme 108

Wiring Diagram (Van - 5.7L With 4L80-E - 1 Of 3). Scheme 109

Wiring Diagram (Van - 5.7L With 4L80-E - 2 Of 3). Scheme 110

Wiring Diagram (Van - 5.7L With 4L80-E - 3 Of 3). Scheme 111