2.8l Pfi "c" Charts Pontiac 6000 I

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 819) 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 819

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" on EFI and terminal "M" on EFI with P-4 systems). These testers can save a great deal of time. For additional information see SCAN TESTER USAGE and SCAN TESTER - TEST DATA PARAMETERS table 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 are: tachometer, test light, ohmmeter, digital voltmeter with 10-megohm 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.

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. 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 the SCAN TESTER - TEST DATA PARAMETERS table below.

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 evidenced, turn ignition off, remove tester, turn ignition on. 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 as information obtained by it may not be accurate.

SCAN TESTER - TEST DATA PARAMETERS

Note. Information in the following tables 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.

PORT FUEL INJECTION

Note. This ECM voltage chart can be used with a digital voltmeter to help save time in diagnosis. Voltages on the car being tested my vary slightly from these due to battery or alternator charging level.

DIAGNOSTIC CIRCUIT CHECK

The diagnostic circuit check is an organized approach for identifying a problem caused by the fuel injection system. Driver comments normally fall into one of the following areas: steady "SERVICE ENGINE SOON" light, driveability problem and engine "CRANKS BUT WON'T RUN".

DIAGNOSTIC CIRCUIT CHECK PROCEDURES

1. Steady "SERVICE ENGINE SOON" light with the ignition on and engine not running confirms battery voltage to the ECM.
2. Code 12 should flash 3 times, followed by any other trouble codes stored in memory.
3. Record all stored trouble codes (except Code 12).
4. With the engine running and the diagnostic terminal grounded, the ECM will respond to the oxygen sensor signal voltage and use the "SERVICE ENGINE SOON" light to display this information as follows: Closed loop confirms the O2 sensor signal is being used by the ECM to control fuel delivery, and the system is working normally. Signal voltage will vary from below .35 to above .55 volts. Open loop indicates that oxygen sensor voltage is unusable to the ECM. Signal voltage is a constant value between .35 and .55 volts. System will flash open loop from 30 seconds to 2 minutes after engine starts or until sensor reaches normal operating temperature. If system fails to go to closed loop, see Code 13. "SERVICE ENGINE SOON" light out indicates lean exhaust. Oxygen sensor signal voltage will be less than .35 volts and steady. "SERVICE ENGINE SOON" light on steady indicates rich exhaust. O2 sensor signal voltage will be greater than .55 volts and steady.
5. Road test of the vehicle using field service mode must be done at steady speeds. In this mode, the following conditions may be observed and are considered normal: light on too long under acceleration, light off too long under deceleration, light on too long with idle below 1200 RPM.
6. Clearing codes. Ignition should be off. Remove continuous battery fuse for 30 seconds. Fuse and holder are located near battery.

Flow Chart, Diagnostic Circuit Check. Scheme 820

Flow Chart, Diagnostic Circuit Check. Scheme 821

"SCAN" DIAGNOSTIC CIRCUIT CHECK

The "SCAN" Diagnostic Circuit Check is an organized approach for identifying fuel injection problems using an Assembly Line Communication Link (ALCL). This communication link can provide diagnostic information for display on any "SCAN" device or tool designed for this purpose.

1. If the "SCAN" tool is not operating, check on another vehicle. If okay, the cigar lighter socket should be checked for 12 volts and a good ground. If the "SCAN" tool reads "no data" or "no ALCL", with the ignition "ON", check the serial data wire for an open or short to ground between ALCL terminal "E" and the ECM. Also check for an open diagnostic test terminal from ALCL terminal "B" and ECM. With ignition on, the serial data line should have a varying 2-5 volts and the diagnostic line about 5 volts.

Flow Chart, "Scan" Diagnostic Circuit Check. Scheme 822

Flow Chart, "Scan" Diagnostic Circuit Check. Scheme 823

Schematic, "Scan" Diagnostic Circuit Check. Scheme 824

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 825

CHART C1A - PARK NEUTRAL SWITCH

Park/Neutral switch contacts are a part of the Neutral Start switch and are closed to ground in park or neutral, and open in drive. The ECM supplies ignition voltage through a current limiting resistor to circuit 434 and senses a closed switch when the voltage on circuit 434 drops to less than 1 volt. The ECM uses the P/N signal as one of the inputs to control, Idle Air Control and VSS Diagnostics.

Note. The following step numbers refer to the numbers on the Diagnostic Flow Charts.

1. This test checks for a closed switch to ground in park position. If using an ohmmeter instead of an test light, the resistance will be low, indicating continuity to ground.
2. This test checks for an open switch in drive range. If using an ohmmeter instead of a test light to 12 volts, the resistance will be high or infinity, indicating an open switch.
3. Checks to this point indicate the P/N switch and wiring are okay, however, the ECM signal voltage on circuit 434 may be mission. To check, reconnect ECM. Either back probe ECM connector circuit 434 with selector in drive or disconnect P/N switch and probe harness connector circuit 434 with a voltmeter to ground.

Flow Chart C1A, Park Neutral Switch. Scheme 826

Flow Chart C1A, Park Neutral Switch. Scheme 827

Schematic C1A, Park Neutral Switch. Scheme 828

CHART C1E - PSPS CHECK

The power steering pressure switch opens when P/S pressure goes high, such as on a full turn in either direction. When the P/S switch opens, it turns the A/C relay off, and sends a signal to the ECM. The ECM uses this signal for idle control.

Note. The following step numbers refer to the numbers on the Diagnostic Flow Charts.

1. This test checks to see that P/S pressure switch opens when pressure goes high.
2. This test checks to see that P/S pressure switch is open.
3. Less than 1 ohm indicates that the switch is closed when the power steering pressure is high. Switch is okay.

Flow Chart C1E, PSPS Check. Scheme 829

Flow Chart C1E, PSPS Check. Scheme 830

Schematic C1E, PSPS Check. Scheme 831

Flow Chart C2C, Idle Air Control. Scheme 832

Flow Chart C2C, Idle Air Control. Scheme 833

Schematic C2C, Idle Air Control. Scheme 834

The ECM will control engine idle speed by moving the Idle Air Control (IAC) valve to control air flow around the throttle plate. It does this by sending voltage pulses to the proper motor winding for each IAC motor. This will cause the motor shaft and valve to move IN or OUT of the motor a given distance for each pulse received. The ECM uses the following information to control idle speed; Battery voltage, Coolant temperature, Manifold Absolute Pressure (MAP), Throttle Position Sensor, Engine speed, A/C clutch signal. Do not apply battery voltage across the ICA motor terminals. This will permanently damage the motor windings.

Note. The following step numbers refer to the numbers on the Diagnostic Flow Charts.

1. 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.
2. Before replacing an ECM, be sure to check the resistance at the IAC motor windings. Failure to do so may result in a repeat ECM failure.

Diagnostic Aids

Engine idle speed can be adversely affected by the following: Faulty P/N switch, leaking injectors, vacuums leaks, binding or sticking throttle shaft or throttle position sensor, faulty EGR valve, faulty battery cables, loss of A/C compressor signal during load.

CHART C3 - CANISTER PURGE CHECK

Canister purge is controlled by a solenoid that allows manifold vacuum to purge the canister when energized. The ECM supplies a ground to energize the solenoid.

Note. The following step numbers refer to the numbers on the Diagnostic Flow Charts.

1. Checks to see if the solenoid is opened or closed. The solenoid is normally energized in this step. It should be closed.
2. This test checks for open or grounded solenoid circuit.
3. Completes functional check by grounding test terminal. This should normally energize the solenoid, allowing vacuum to drop.
4. Determines if ECM control circuit or solenoid is at fault.

Flow Chart C3, Canister Purge Check. Scheme 835

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.

Flow Chart C3, Canister Purge Check. Scheme 836

Schematic C3, Canister Purge Check. Scheme 837

CHART C4B - IGNITION SYSTEM CHECK

Note. The following step numbers refer to the numbers on the Diagnostic Flow Charts.

1. 1) Two wires are checked, to ensure that an open is not present in a spark plug wire.
2. 1A) If spark occurs with EST connector disconnected, pick-up coil is too low for EST operation.
3. 2) A spark indicates that the problem is a faulty distributor cap or rotor.
4. 3) Normally, there should be battery voltage at the "C" and "+" terminal. Low voltage would indicate an open or high resistance circuit from the distributor to coil or ignition switch. If "C" terminal voltage was low, but "+" terminal voltage is 10 volts to more, circuit from "C" terminal to ignition coil or ignition coil primary winding is open.
5. 4) This test 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 1 volt. This could cause the ignition coil to fail from excessive heat. With an open ignition coil primary winding, a small mount of voltage will leak through the module from the "BAT" to the tach terminal.
6. 5) This test checks for an open module or circuit to it. Applying 1.5 to 8 volts to the terminal "P" will turn the module "ON" and the voltage should drop to about 7-9 volts.
7. 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 at fault.

Flow Chart C4B, Ignition System Check. Scheme 838

Flow Chart C4B, Ignition System Check (1 Of 2). Scheme 839

Flow Chart C4B, Ignition System Check (2 Of 2). Scheme 840

Schematic C4B, Ignition System Check. Scheme 841

CHART C6A - ELECTRIC DIVERT (W/ MAN. TRANS.)

This system uses a single bed converter and Air Management is controlled by an air control valve (divert valve). When grounded by the ECM, the solenoid causes the valve to direct air to exhaust ports. When de-energized air diverts to the atmosphere. Air goes to the ports provided the valve has a ground to the ECM and good manifold vacuum.

Note. The following step numbers refer to the numbers on the Diagnostic Flow Charts.

1. This is a system performance test. When vehicle goes to closed loop, air will switch from the ports to divert.
2. Tests for a grounded electric divert circuit. Normal system light will be off.
3. This test checks for an open control circuit. Grounding test terminal will energize the solenoid if ECM and circuits are normal. In this step, if test light is on, circuits are normal and fault is in valve connections or valve.

Flow Chart C6A, Electric Divert (W/ Man. Trans.). Scheme 842

Flow Chart C6A, Electric Divert (W/ Man. Trans.). Scheme 843

Schematic C6A, Electric Divert (W/ Man. Trans.). Scheme 844

CHART C7A - EXHAUST GAS RECIRCULATION

EGR valve is controlled by a normally closed solenoid (allows vacuum to pass when energized). The ECM energizes the solenoid to turn the EGR on, and monitors vacuum to the EGR with the EGR diagnostic switch. Code 32 will detect a faulty solenoid, vacuum switch or vacuum supply.

Note. The following step numbers refer to the numbers on the Diagnostic Flow Charts.

1. With ignition switch "ON" and engine stopped, the solenoid should not be energized and vacuum should not pass to the EGR valve.
2. Grounding the diagnostic terminal will energize the solenoid and allow vacuum to pass to the valve.
3. This test checks for plugged EGR passages. If passages are plugged, the engine may have severe detonation on acceleration.
4. The EGR solenoid will not be energized in Park or Neutral. This test determines if the P/N switch input is recognized by the ECM.

Flow Chart C7A, Exhaust Gas Recirculation. Scheme 845

Flow Chart C7A, Exhaust Gas Recirculation. Scheme 846

Schematic C7A, Exhaust Gas Recirculation. Scheme 847

CHART C8 - TRANS. CONV. CLUTCH (ALL TRANS./TRANSAXLES)

Fused battery ignition is supplied to the TCC Solenoid through the brake switch, and transmission/transaxle third gear apply switch. The ECM will engage TCC by grounding circuit 422 to energize the solenoid. TCC sill engage when: Engine is warmed up. Vehicle speed is above calibrated Throttle Position Sensor (TPS) output not changing, indicating a steady road speed. Transaxle third gear apply switch is closed. Brake switch is closed.

Note. The following step numbers refer to the numbers on the Diagnostic Flow Charts.

1. Light off confirms transmission/transaxle third gear supply switch is open.
2. At 20-25 MPH the transmission/transaxle third gear switch should close. Test light will come on and confirm battery supply and closed brake switch.
3. Grounding the diagnostic terminal with engine "OFF" should energize the TCC solenoid. This test checks the capability of the ECM to control the solenoid.
4. Solenoids and relays are turned "ON" and "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.

Flow Chart C8, TCC (All Transmissions/Transaxles). Scheme 848

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

Scheme 849

Scheme 850

1. Coolant Temperature
2. TPS
3. VSS
4. Codes - If 24 Is Present, See Code Chart 24. Also, Perform Mechanical Checks Such As Linkage, Oil Level, Etc., Before Using This Chart. (Scheme 849): Flow Chart C8, TCC (All Transmissions/Transaxles) (Scheme 850): Schematic C8, TCC (All Transmissions/Transaxles)

CHART C8A - TRANS. CONV. CLUTCH (CONT.)(125-C TRANSAXLE)

Fused battery ignition is supplied to the TCC Solenoid through the brake switch, and transmission/transaxle third gear apply switch. The ECM will engage TCC by grounding circuit 422 to energize the solenoid. TCC will engage when: Engine is warmed up. Vehicle speed is above calibrated Throttle Position Sensor (TPS) output not changing indicating a steady road speed. Transaxle third gear apply switch is closed. Brake switch is closed.

Note. The following step numbers refer to the numbers on the Diagnostic Flow Charts.

1. Light off confirms transmission/transaxle third gear supply switch is open.
2. At 20-25 MPH the transmission/transaxle third gear switch should close. Test light will come on and confirm battery supply and closed brake switch.
3. Grounding the diagnostic terminal with engine "Off" should energize the TCC solenoid. This test checks the capability of the ECM to control the solenoid.
4. Solenoids and relays are turned "ON" and "OFF" by the ECM internal electronic switches called "drivers". Each driver is part of a group within the set.

Flow Chart C8A, TCC (Continued for W/ 125-C Trans.). Scheme 851

Flow Chart C8A, TCC (Continued for W/ 125-C Trans.). Scheme 852

Schematic C8A, TCC (Continued for W/ 125-C Trans.). Scheme 853

CHART C10A - A/C CLUTCH CONTROL

The A/C clutch control relay is ECM controlled to Delay A/C clutch engagement .4 seconds after A/C is turned on. This allows the IAC to adjust engine RPM before the A/C clutch engages. The ECM also causes the relay to disengage the A/C clutch during WOT operation. The A/C clutch control relay is energized when the ECM provides a ground path for circuit 905.

Note. The following step numbers refer to the numbers on the Diagnostic Flow Charts.

1. Checks to see if the ECM is controlling the A/C clutch control relay.
2. This test checks operation of A/C cycling switch.
3. This test checks for grounded circuit 905 to ECM. At this point the test light should be off.
4. If the ECM recognizes a high power steering pressure the A/C clutch relay will be de-energized. The ECM will pulse circuit 905 on and off to de-energize the relay. This would cause a blinking test light when circuit 905 was tested.

Flow Chart C10A, A/C Clutch Control. Scheme 854

Flow Chart C10A, A/C Clutch Control. Scheme 855

Schematic C10A, A/C Clutch Control. Scheme 856

CHART C10B - A/C CLUTCH CONTROL

Note. The following step numbers refer to the numbers on the Diagnostic Flow Charts.

1. This test checks for battery voltage to relay through circuit 59.
2. Substitutes for relay to determine if problem is in relay or in circuit 59, A/C clutch coil, high press, switch or ground.
3. This test checks for open in circuit 59 between cycling switch and A/C fuse or open circuit 59 to relay.
4. This test checks to see that "A/C ON" signal is getting to ECM through circuit 59. A test light off at this time indicates circuit 59 is open between the cycling switch and the ECM.

Flow Chart C10B, A/C Clutch Control. Scheme 857

Flow Chart C10B, A/C Clutch Control. Scheme 858

CHART C12A - COOLANT FAN CHECK

The cooling fan is totally controlled by the ECM based on inputs from the coolant sensor and fan switch. The fan should run if coolant temperature is greater than 234°F (112°C).

Battery voltage is supplied to the fan relay on terminal "E"and ignition voltage to terminal C. Grounding circuit 335 (relay terminal "B") will energize the relay and supply battery voltage to the fan motor. The ECM will remove the ground to circuit 335 if vehicle speed is over 40 MPH unless the engine is overheating. When A/C is used, the fan control switch mounted in the A/C High pressure line will open when head pressure exceeds 233 psi. and this input causes the ECM to ground circuit 335. If coed 14 or 15 sets, the ECM will turn on the cooling fan. If the ECM fails to turn on the Fan Relay by grounding circuit 335, the fan override switch can complete the circuit.

Chart C12C, Coolant Fan Check. Scheme 859

Chart C12C, Coolant Fan Check. Scheme 860

Schematic C12C, Coolant Fan Check. Scheme 861

Component Locations (A Body). Scheme 862

Component Locations (F Body). Scheme 863

Component Locations (P Body). Scheme 864

ECM Terminal Identification (Except Fiero). Scheme 865

ECM Terminal Identification (Fiero). Scheme 866

FWD PFI CCC Wiring Diagram. Scheme 867

RWD PFI CCC Wiring Diagram. Scheme 868

Fiero PFI CCC Wiring Diagram. Scheme 869