1987-88 Computerized Engine Controls Chevrolet Camaro III рестайлинг

MODEL IDENTIFICATION

Repair procedures in this article are sometimes identified by a specific body code. The following table lists GM division, model name, and body types that apply to the body codes.

MODEL IDENTIFICATION

DESCRIPTION

The computerized engine control system monitors as many as 19 engine/vehicle functions. (Scheme 437) This system controls engine operation and lowers exhaust emissions while maintaining fuel economy and driveability. The Electronic Control Module (ECM) is the "brain" of the CCC system.

The computerized engine control system is primarily an emission control system, designed to maintain a 14.7:1 air/fuel ratio under all operating conditions. When the ideal air/fuel ratio is maintained, the 3-way catalytic converter can control Oxides of Nitrogen (NOx), Hydrocarbon (HC) and Carbon Monoxide (CO) emissions.

ECM Conditions Sensed & Systems Controlled. Scheme 437

SPECIAL DIAGNOSTIC TOOLS

Note. Special "Scan" testers plugged into the ALDL may be used to read trouble codes and check voltages in the system on the serial data line (terminal "E") These testers can save a great deal of time. For additional information see SCAN TESTER USAGE and SCAN TESTER - TEST DATA PARAMETERS tables in this article.

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 impedance (minimum), vacuum pump, vacuum gauge, fuel injector test lights (TBI and PFI) 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.

SCAN TESTER USAGE

Note. Prior to connection of scan tester to vehicle, diagnostic system should be checked to determine if system is operating properly and if information received by scan tester will be accurate. This is done by performing appropriate DIAGNOSTIC CIRCUIT CHECK for that system. If vehicle does not pass diagnostic circuit check, information received by scan tester may be invalid. CCC Scan tester is a specialized tester which, when plugged into ALDL, can be used to diagnose on-board computer control stems by providing instant access to circuit voltage information without need to crawl under dash or hood to back-probe sensors and connectors.

Scan testers cut down diagnostic time dramatically by furnishing input data (voltage signals) which can be compared to specification parameters. See SCAN TESTER - TEST DATA PARAMETERS table in this article. They also furnish information on output device (solenoids and motors) status. Status parameters, however, are only an indication that output signals have been sent to devices by the ECM. It does not indicate if devices have responded properly to that signal. This will need to be verified at output device using a voltmeter or test light.

Note. Code 12 should always exist when ALDL is grounded with key on and engine not running but may not be indicated by all makes of scan tester.

If trouble codes are not present, this is not an indication that there is not a problem. CCC related problems are about 20 percent codes and 80 percent driveability. Sensors that are out of specification WILL NOT set a trouble code but WILL cause driveability problems. Use of a scan tester is 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 - TEST DATA PARAMETERS table in this article.

Note. Information obtained by scan tester is only as accurate as the tester itself. If erroneous voltage signals are suspected, it will be necessary to verify tester information using a digital voltmeter and wiring schematic. If non- existent codes are in evidence, turn ignition off, remove tester, turn ignition on and ground ALDL "DIAGNOSTIC TERMINAL". If same codes are not flashed by "SERVICE ENGINE SOON" light that were indicated by scan tester, tester cannot be used on vehicle and information obtained by it will not be guaranteed accurate.

SCAN TESTER - TEST DATA PARAMETERS

Note. Information in the following table is typical readings taken on vehicle with engine idling, upper radiator hose hot, closed throttle, transmission in Park or Neutral, "closed loop" status achieved and all accessories off (except as noted in tables). Data parameters are updated every 1 1/4 seconds. On systems using P-4 computers, parameter updates are virtually instantaneous. Not all devices & systems are used on all models.

THROTTLE BODY INJECTION

"NON-SCAN" DIAGNOSTIC CIRCUIT CHECK

The diagnostic circuit check is an organized approach for identifying a problem caused by the fuel injection system. Driver complaints fall into 3 categories: steady "SERVICE ENGINE SOON" light, driveability problems, and "engine cranks, but will not run". Understanding chart and using it correctly will reduce diagnostic time and prevent unnecessary replacement of parts.

Note. The following step numbers refer to the numbers in the accompanying flow chart(s).

1. A steady "SERVICE ENGINE SOON" light with ignition on and engine not running confirms battery and ignition voltage to Electronic Control Module (ECM).
2. Ground diagnostic test terminal by connecting a jumper wire between terminals "A" and "B" in assembly line communication link (ALCL) connector, located below instrument panel. The ECM will cause "SERVICE ENGINE SOON" light to flash Code 12, indicating that ECM diagnostics are working. Code 12 will flash 3 times, followed by other trouble codes stored in memory. Each additional code will flash 3 times, starting with lowest code, and then start over again with Code 12. If there are no other codes, Code 12 will flash until diagnostic test terminal jumper is disconnected or engine is started.
3. Record all stored codes, except Code 12. If the problem is "engine cranks but will not run", proceed to CHART A3.
4. If no additional codes were recorded, see TROUBLE SHOOTING procedures in CEC TESTS W/O CODES article in this section for driveability symptoms and recommended service procedures. With engine running and diagnostic terminal grounded, the ECM will respond to the oxygen sensor signal and use the "SERVICE ENGINE SOON" light to display the following information: A) Closed loop confirms that oxygen sensor signal is being used by the ECM to control fuel delivery and that system is working properly. Signal voltage will vary from below .35 to above .55 volts. B) Open loop indicates that oxygen sensor signal is not useable to ECM. Signal voltage will be constant and between 35 and .55 volts. System will flash "open loop" for 30 seconds to 2 minutes after engine starts or until sensor reaches normal operating temperature. If system fails to go into closed loop, see Code 13 test. C) "SERVICE ENGINE SOON" light off indicates that exhaust is lean. Oxygen sensor will be less than .35 volts and steady. See Code 44 test procedures. D) "SERVICE ENGINE SOON" light on steady indicates that exhaust is rich. Oxygen sensor signal will be above .55 volts and steady. See Code 45 test procedures.
5. Road test of the system in the field service mode should be done only at steady road speeds. The following conditions may be observed and should be considered normal: light on too long under acceleration, light off too long under deceleration or light on too long with idle below 1200 RPM.
6. To clear codes, turn ignition off and disconnect battery pigtail for 10 seconds

"Non-Scan" Diagnostic Circuit Check. Scheme 438

"SCAN" DATA DIAGNOSTIC CIRCUIT CHECK

The Diagnostic Circuit Check is an organized approach to identifying a problem created by an Electronic Engine Control System (EECS) malfunction. It must be the starting point for driveability complaint diagnosis, because it directs the service technician to the next logical step in diagnosing the complaint.

The "SCAN DATA" chart may be used for comparison, after completing the diagnostic circuit check and finding the on-board diagnostics functioning properly and no trouble codes displayed. The typical values are an average of display values recorded from normally operating vehicles and are intended to represent what a normally functioning system would typically display.

Note. A "SCAN" tester that displays faulty data should not be used, and the problem should be reported to the manufacturer. The use of a faulty "SCAN" tester can result in misdiagnosis and unnecessary parts replacement.

Only the parameters listed are used in this article for diagnosis. If a "SCAN" tester reads other parameters, the values are not recommended by General Motors for use in diagnosis.

"Scan" Data Diagnostic Circuit Check. Scheme 439

CHART C1 - ECM REPLACEMENT CHECK CHART

In order to reduce incidents of repeat ECM failure, a revised ECM 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

Scheme 440

CHART C1A - PARK/NEUTRAL SWITCH DIAGNOSIS (AUTO TRANS.)

The park/neutral switch is closed to ground in park or neutral, and open in drive ranges. The ECM supplies 12 volts through an internal resistor to circuit No. 434 and senses that switch is closed when voltage at terminal B10 drops to less than one volt.

Note. Test numbers refer to test numbers on diagnostic chart.

1. Checks for a closed switch to ground in park position. Different makes of "SCAN" tester will read P/N differently. Refer to "SCAN" tester operations manual for type of display used.
2. Checks for an open switch in drive range.
3. Be sure "SCAN" tester indicates drive, even while wiggling shifter to test for an intermittent or misadjusted switch in drive range.

Flow Chart C1A, Park/Neutral Switch Diagnosis (Auto. Trans.). Scheme 441

CHART C1B - CRANK SIGNAL

Crank signal is a 12-volt signal to ECM during cranking to allow enrichment and cancel diagnostics until engine is running or 12 volt is no longer on circuit.

1. Checks for normal (cranking) voltage to terminal C9 of ECM. Test light should be on during cranking.
2. Determines if source of blown fuse was a faulty ECM.

Flow Chart C1B, Crank Signal. Scheme 442

CHART C1D - MAP OUTPUT CHECK

The MAP measures manifold pressure (vacuum) and sends that signal to ECM. ECM uses this information for fuel and spark control.

1. Checks MAP sensor output voltage to ECM. This voltage, without engine running, represents a barometer reading to ECM.
2. Applying 10 in. Hg (34 kPa) vacuum to MAP sensor should cause voltage to be 1.2 volts less than voltage at step 1). Upon applying vacuum to sensor, change in voltage should be instantaneous. A slow voltage change indicates a faulty sensor.
3. Check vacuum hose to sensor for leaking or restriction. Be sure no other vacuum devices are connected to MAP hose.

Flow Chart C1D, MAP Output Check. Scheme 443

IGNITION ON, ENGINE OFF VOLTAGES (LOW ALTITUDE = HIGH PRESSURE = HIGH VOLTAGE)

CHART C2C - IDLE AIR CONTROL

The ECM controls idle rpm with the IAC valve. To increase idle rpm, the ECM moves the IAC valve out, allowing more air to pass by throttle plate. To decrease rpm, it moves the IAC valve in, reducing airflow by the throttle plate. A "SCAN" tester will read the ECM commands to the IAC valve in counts. The higher the count, the more air allowed (higher idle). The lower the count, the less air allowed (lower idle).

Note. Test numbers refer to test numbers on diagnostic chart.

1. Continue with test, even if engine will not idle. If idle is too low, "SCAN" tester will display 80 or more counts (or steps). If idle is high, it will display "0" counts. Occasionally, an erratic or unstable idle may occur. Engine speed may vary 200 rpm, or more, up and down. Disconnect IAC. If the condition is unchanged, the IAC is not at fault.
2. When the engine was stopped, the IAC valve retracted (more air) to a fixed "Park" position for increased airflow and idle speed during the next engine start. A "SCAN" tester will display 100 or more counts. When performing this test, immediately note rpm on start up, on warm engine, the rpm will decrease rapidly.
3. Be sure to disconnect the IAC valve prior to this test. The test light will confirm the ECM signals by a steady or flashing light on all circuits.
4. There is a remote possibility that one of the circuits is shorted to voltage, which would have been indicated by a steady light. Disconnect ECM and turn the ignition on and probe terminals to check for this condition.

Diagnostic Aids

A slow unstable idle may be caused by a system problem that cannot be overcome by the IAC. The "SCAN" tester counts will be above 60 counts, if too low, and "0" counts, if too high.

If idle is too high, stop engine. Turn ignition on and ground diagnostic cable. Wait 30 seconds for IAC to seat then disconnect IAC. Unground diagnostic terminal and start engine. If idle speed is above 450 rpm in drive, locate and correct vacuum leak. If rpm is less than 450 rpm, adjust minimum idle speed or correct other conditions, which may affect idle.

1. Idle speed may be too high or too low. Engine speed may vary up and down, disconnecting IAC does not help. This may set Code 44. A "SCAN" tester and/or voltmeter will read an oxygen sensor output less than .3 volts. Check for low regulated fuel pressure or water in fuel. A lean exhaust, with an oxygen sensor output fixed above .8 volts, will be a contaminated sensor. This may also set Code 45.
2. Idle speed too low. If "SCAN" tester counts are above 80, system obviously rich and may exhibit Black smoke from the exhaust. The "SCAN" tester and/or voltmeter will read an oxygen sensor signal fixed above .8 volts. Check for high fuel pressure and/or injector leaking or sticking.
3. Remove IAC and inspect bore for foreign material or evidence of IAC valve dragging in the bore.

Flow Chart C2C, Idle Air Control (IAC). Scheme 444

CHART C3 - CANISTER PURGE CHECK

Canister purge is controlled by a solenoid that allows manifold vacuum to purge canister when de-energized. The ECM supplies a ground to energize solenoid (purge off). If diagnostic test terminal is grounded with engine stopped with engine running, purge solenoid is de-energized (purge on).

Note. Test numbers refer to test numbers on diagnostic chart.

1. Checks to see if the solenoid is opened or closed. The solenoid is, normally energized in this test, so it should be closed.
2. Checks for a complete circuit. Normally, there is battery voltage on circuit No. 39, and the ECM provides a ground on circuit No. 428. A shorted solenoid could cause an open circuit in the ECM.
3. Completes functional check, by grounding test terminal. Normally this should de-energize the solenoid and allow the vacuum to drop (purge "ON").
4. Solenoids, or relays, are turned on or off by the ECM internal electronic switches, called "Drivers". Each driver is part of a group of 4 called "Quad-Drivers". Failure of one can damage any other driver within the set. Solenoid coil resistance must measure more than 20 ohms. Less resistance will cause early failure of the ECM "Driver". Using an ohmmeter, check solenoid coil resistance of all ECM controlled solenoids and relays before installing a replacement ECM.

Flow Chart C3, Canister Purge Check. Scheme 445

Note. This chart only covers the solenoid portion of the Canister Control Purge system. To test the control valve(s), see diagnosis under general description.

Note. Before replacing ECM use ohmmeter and check resistance of each ECM controlled relay and solenoid coil. See ECM wiring diagram for coil terminal identification for solenoid(s) and relay(s) to be checked. Replace any relay or solenoid if the coil resistance measures less than 20 ohms.

CHART C4B - IGNITION SYSTEM CHECK

Note. Test numbers refer to test numbers on diagnostic chart.

1. Two wires are checked, to ensure that an open is not present in a spark plug wire. If spark occurs with EST connector disconnected, pick-up coil output is too low for EST operation.
2. A spark indicates the problem must be the distributor cap or the rotor.
3. Normally, there should be battery voltage at the "C" and "plus" terminals. Low voltage would indicate an open or a high resistance circuit from the distributor to the coil or ignition switch. If "C" terminal voltage was low, but "plus" terminal voltage is 10 volts or more, circuit from "C" terminal to ignition coil or ignition coil primary winding is open.
4. Checks for a shorted module or grounded circuit from the ignition coil to the module. The distributor module should be turned off, so normal voltage should be about 12 volts. If the module is turned on, the voltage would be low, but above one volt. This could cause the ignition coil to fail from excessive heat. With an open ignition coil primary winding, a small amount of voltage will leak through the module from the battery to the tachometer terminal.
5. Applying 1.5-8 volts to module terminal "P" should turn the module on. The tachometer terminal voltage should drop to about 7-9 volts. This test will determine whether the module or coil is faulty or if the pick-up coil is not generating the proper signal to turn the module on. This test can be performed by using a DC battery with a rating of 1.5-8 volts. The use of the test light is mainly to allow the "P" terminal to be probed more easily. Some digital multi-meters can also be used to trigger the module by selecting ohms, usually in the diode position. In this position the meter may have voltage across its terminals which can be used to trigger the module. The voltage in the ohm position can be checked by using a second meter or by checking the manufacturer's specification of the "SCAN" tester being used.
6. This should turn off the module and cause a spark. If no spark occurs, the fault is most likely in the ignition coil because most module problems would have been found before this point in the procedure. A module tester could determine which is a fault.

Flow Chart C4B, Ignition System Check. Scheme 446

CHART C5 - ELECTRONIC SPARK CONTROL (ESC) CHECK

Electronic Spark Control (ESC) is accomplished with a module that sends a voltage signal to the ECM. As the knock sensor detects engine knock, voltage from the ESC module to the ECM is shut off. This signals the ECM to retard timing, if engine speed is over 900 rpm.

Note. Test numbers refer to test numbers on diagnostic chart.

1. If a Code 43 is not set, but a knock signal is indicated while running at 1500 rpm, listen for an internal engine noise. Under a no load condition, there should not be any detonation, and if knock is indicated, an internal engine problem may exist.
2. Usually a knock signal can be generated by tapping on the right exhaust manifold. This test can also be performed at idle. Test No. 1 was run at 1500 rpm, to determine if a constant knock signal was present, which would affect engine performance.
3. This will test whether the knock signal is due to the sensor, a basic engine problem, or the ESC module.
4. If the module ground circuit is faulty, the ESC module will not function correctly. The test light should light indicating the ground circuit is okay.
5. Using a test light with 12 volts at circuit No. 496 should generate a knock signal to determine whether the knock sensor is faulty, or the ESC module can't recognize a knock signal.

Flow Chart C5, Electronic Spark Control (ESC) Check. Scheme 447

CHART C6B - AIR MANAGEMENT CHECK (PEDES VALVE)

Air management is controlled by a port valve and a converter valve, each with an ECM controlled vacuum solenoid. When solenoid is grounded by ECM, air pressure will activate valve and allow pump air to be directed either to the solenoid that is grounded or port solenoid that may be also grounded.

Note. Test numbers refer to test numbers on diagnostic chart.

1. This is a system functional check. Air is directed to ports during "open loop" and all engine starts are in open loop (even on a warm engine). Since the air to the ports time is very short on some engines, prepare to observe port air prior to engine start up. On some engines, this can be done by squeezing a hose. On others, steel pipes have to be disconnected.
2. This should normally set a Code 22. When any code is set, the ECM opens the ground to the air control valve and allows air to divert. This checks for ECM response to a fault that may exist. A ground in the control valve circuit to the ECM would prevent diverter action.
3. This checks for a ground circuit to the ECM. If test light is off, this is normal and would indicate the circuits are not grounded.
4. Checks for an open in the solenoid control circuits. Grounding the test terminal should ground both solenoid circuits. Normally, the test light should be on which indicates the problem is not in the ECM or wiring but at the solenoid connections or the switching valve itself.
5. Checks for a grounded switching valve circuit. If test light is off, this would indicate the circuit is normal and fault is in the switching valve.

Flow Chart C6B, Air Management Check (Pedes Valve). Scheme 448

CHART C7 - EGR CHECK

The ECM operates a solenoid to control the EGR valve. This solenoid is normally closed. By providing a ground path, the ECM energizes the solenoid which then allows vacuum to pass to the EGR valve. The ECM control of the EGR is based on the following inputs

1. Engine coolant temperature above 25°C.
2. TPS idle.
3. MAP.

Note. Test numbers refer to test numbers on diagnostic chart.

1. Checks for a stuck open solenoid.
2. Checks for solenoid always being energized.
3. Grounding test terminal should energize solenoid and vacuum should drop.
4. Negative backpressure valve should hold vacuum with the engine off.
5. When the engine is started, exhaust backpressure should cause vacuum to bleed off and valve to fully close.

Flow Chart C7, EGR Check. Scheme 449

Note. Before replacing ECM use ohmmeter and check resistance of each ECM controlled relay and solenoid coil. See ECM wiring diagram for coil terminal identification for solenoid(s) and relay(s) to be checked. Replace any relay or solenoid if the coil resistance measures less than 20 ohms.

200-4R TORQUE CONVERTER CLUTCH (TCC) DIAGNOSIS (1 OF 2)

The purpose of automatic transmission torque converter clutch feature is to eliminate power loss of torque converter stage when vehicle is in cruise condition. This allows convenience of automatic transmission and fuel economy of a manual transmission. Fused battery ignition is supplied to TCC solenoid through brake switch. The ECM will engage TCC by grounding circuit No. 422 to energize the solenoid. TCC engages when vehicle speed is above 24 MPH, engine is at normal operating temperature, throttle position sensor output not changing (indicating steady road speed), and/or brake switch is closed.

Note. Test numbers refer to test numbers on diagnostic chart.

1. Confirms 12-volt supply as well as continuity of TCC circuit.
2. Grounding the diagnostic terminal with engine off, should energize the capability of the ECM to control the solenoid
3. Solenoid coil resistance must measure more than 20 ohms. Less resistance will cause early failure to the ECM "driver". Using an ohmmeter, check the solenoid coil resistance of all ECM controlled solenoids and relays before installing a replacement ECM. Replace any solenoid or relay that measures less than 20 ohms.

An engine coolant temperature coolant thermostat that is stuck open or opens at too low a temperature, may result in an inoperative TCC. If TCC engages before "SCAN" indicates solenoid or sump over temperature switch may be faulty.

Flow Chart C8A, 200-4R TCC Electrical Diagnosis. Scheme 450

Using A "Scan" Tool, Check The Following And Correct If Necessary

1. Coolant Temperature Should Be Above 65°C
2. TPS - Be Sure TPS Signal Is Not Erratic
3. VSS - Be Sure "Scan" Displays VSS With Drive Wheels Turning, If Code 24 Is Present, See Code Chart 24

200-4R TORQUE CONVERTER CLUTCH (TCC) DIAGNOSIS (2 OF 2)

Note. Test numbers refer to test numbers on diagnostic chart.

1. Unless switch or circuit No. 446 is open, the "SCAN" tester should display "NO", indicating the transmission is not in 4th gear. The 4th gear switch should only be open while in 4th gear.
2. This test determines if the ECM and wiring are okay. Grounding circuit No. 446 should cause the "SCAN" to display "NO", indicating the transmission is not in 4th gear.
3. Checks operation of the 4th gear switch. When the transmission shifts into 4th gear the switch should open and the "SCAN" should display "YES".
4. Disconnecting the TCC connector simulates an open switch to determine if circuit No. 446 is shorted to ground or the problem is in the transmission.

A road test may be necessary to verify customer complaint. If the "SCAN" tester indicates TCC is turning "ON" and "OFF" erratically, check the state of the 4th gear switch to be sure it is not changing states under a steady throttle position. If the switch is changing, check connections and wire routing carefully. Also if 4th gear switch is always open, the TCC may engage as soon as sufficient oil pressure is reached.

Flow Chart C8A (2 of 2), TCC Electrical Diagnosis. Scheme 451

Note. Checks made in this chart will not prevent the TCC from working, but will affect engagement or disengagement points.

5.0L TBI Component Locations ("F" Body). Scheme 452

5.0L TBI ECM Terminal ID & Pin Voltages ("F" Body). Scheme 453

5.0L TBI CCC Wiring Diagram (1988 "F" Body). Scheme 454