2.5l Tbi "a" Charts Pontiac 6000 I

MODEL IDENTIFICATION

Repair procedures in this article are identified by body type. The following table lists GM division, model name, and body type.

MODEL IDENTIFICATION

DESCRIPTION

Note. Most Computer Command Control (CCC) problems are the result of mechanical breakdowns, poor electrical connections or damaged vacuum hoses. Before considering the CCC system as a possible cause of problems, ignition high tension wires, fuel supply, electrical connections and vacuum hoses should be checked. Failure to do so may result in lost diagnostic time.

The Computer Command Control (CCC) system used on the 1985 General Motors vehicles monitors as many as 19 engine/vehicle functions. This system controls engine operation and lowers exhaust emissions while maintaining good fuel economy and driveability. The Electronic Control Module (ECM) is the "brain" of the CCC system. The ECM controls as many as 12 engine related systems constantly adjusting engine operation.

The CCC 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 catalytic converter can control oxides of nitrogen (NOx), hydrocarbon (HC) and carbon monoxide (CO) emissions.

ECM Operating Conditions Sensed & Systems Controlled. Scheme 703

Schematic of Computer Command Control System. Scheme 704

Sectional View of Mixture Control Solenoid. Note air bleed above main metering rod. Scheme 705

DIAGNOSTIC TOOLS

The CCC system does not require special tools for diagnosis. A tachometer, a dwell meter, test light, ohmmeter, digital voltmeter with 10 megohms impedance (minimum), vacuum pump, vacuum gauge and 6 jumper wires 6" long (1 wire with female connectors at both ends; 1 wire with male connector at both ends; 4 wires with male and female connectors at opposite ends) are the only tools necessary for diagnosis.

Note. Special testers can be used to read trouble codes and check voltages in the system. These tools can save a great deal of time, but are not required. Refer to tester manual for operating procedures.

A test light, rather than a voltmeter, must be used when indicated by a diagnostic chart.

On carbureted models, the dwell meter is used to measure the time the M/C solenoid is on or off. This indicates if the M/C solenoid is working and the fuel mixture strength (rich or lean). The dwell meter is set on the 6-cylinder scale regardless of the number of cylinders in the engine.

Dwell meter is connected to Green connector located near the carburetor. This connector will not be connected to any circuit EXCEPT when you are testing with the dwell meter. DO NOT allow terminal wire to come in contact with any ground source, including rubber hoses.

Note. If engine operation seems to change when the dwell meter is connected to Green wire, remove dwell meter and use another type. A few brands are not compatible with CCC system.

If engine is at operating temperature and idling, dwell meter needle should be varying between 10-50°. This indicates closed loop operation. If needle does not move, open loop operation is indicated.

"NONSCAN" DIAGNOSTIC CIRCUIT CHECK (A/F/N/P BODY)

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 the chart and using it correctly will reduce diagnostic time and prevent unnecessary replacement of parts.

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 the CCC 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: 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. 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. "SERVICE ENGINE SOON" light off indicates that exhaust is lean. Oxygen sensor will be less than .35 volts and steady. See Code 44. "SERVICE ENGINE SOON" light on steady indicates that exhaust is rich. Oxygen sensor signal will be above .55 volts and steady. See Code 45.
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.

"NONSCAN" Diagnostic Circuit Check Flow Chart (All). Scheme 706

"NONSCAN" Diagnostic Circuit Check Flow Chart (All). Scheme 707

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 DATA tables. 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 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 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.

THROTTLE BODY INJECTION

"SCAN" DIAGNOSTIC CIRCUIT CHECK (A/F/J/N/P BODY)

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. The tool plugs into ALCL connector located below instrument panel. If a stored code is displayed, code definitions will aid in determining if fault is still present (hard failure) or result of an intermittent condition not normally diagnosed using code charts.

1) If 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 scan tool reads "no data" or "no ALCL" with ignition on, check serial data wire for an open or short to ground between ALCL terminal "E" and ECM. Also check for an open diagnostic test terminal for ALCL terminal "B" and ECM. With ignition on, serial data line (ALCL terminal "E") should have a varying 2-5 volts, and diagnostic line (ALCL terminal "B") about 5 volts.

"Scan Diagnostic Circuit Check Flow Chart (All). Scheme 708

"Scan Diagnostic Circuit Check Flow Chart (All). Scheme 709

CHART A1 - NO "SES" LIGHT (A/F/J/N/P BODY)

The "SERVICE ENGINE SOON" light should come on when ignition is turned on and engine is not running. Battery voltage is supplied directly to the bulb. The ECM controls the light by grounding circuit No. 419.

If engine runs, a no "SERVICE ENGINE SOON" light condition indicates a defective bulb, blown fuse or open control circuit No. 419. If engine cranks but will not run, no "SERVICE ENGINE SOON" light indicates a blown battery fuse, blown fusible link, ECM ignition fuse blown, battery circuit No. 340 to ECM open, ignition circuit No. 439 to ECM open or poor connection to ECM.

1) Solenoids and relays are turned on or off by ECM, using electronic switches called "drivers". Each driver is part of a group of 4, called "QuaDDrivers". Failure of one (1) driver can damage other drivers in set. Solenoid and relay coil resistance must be more than 20 ohms, as less resistance will cause early failure of ECM drivers.

Flow Chart A1: No "SES" Light (All Models). Scheme 710

Flow Chart A1: No "SES" Light (All Models). Scheme 711

CHART A2 - NO CODE 12, "SES" ALWAYS ON (A/F/J/N/P BODIES)

The "SERVICE ENGINE SOON" light should come on when ignition switch is in the "ON" position and engine is not running. Battery voltage is directly supplied to bulb. The ECM controls the light by grounding circuit No. 419. With diagnostic terminal grounded, light should flash Code 12, followed by other trouble codes stored in memory. A steady light indicates a grounded circuit No. 419 or an open diagnostic circuit No. 451.

1. If the light goes off when the ECM connector is disconnected, then circuit No. 419 is not shorted to ground. Check connector terminals physically for proper contact.
2. This step checks for an open diagnostic circuit No. 451.
3. At this point wiring is okay. Problem may be a faulty ECM or PROM. If Code 51 is stored when PROM is removed, replace PROM.
4. Solenoids and relays are turned on or off by ECM, using electronic switches called "drivers". Each driver is part of a group of 4, called "QuaDDrivers". Failure of one (1) driver can damage other drivers in set. Solenoid and relay coil resistance must be more than 20 ohms, as less resistance will cause early failure of ECM drivers.

Flow Chart A2: No Code 12, "SES" Light on Steady (All). Scheme 712

Flow Chart A2: No Code 12, "SES" Light on Steady (All). Scheme 713

CHART A3 - CRANKS BUT WON'T RUN (A/F/J/N/P BODY)

1. A "SERVICE ENGINE SOON" light on checks for ignition and battery supply to ECM.
2. Fuel spray from injector indicates that fuel is available, check engine for flooding.
3. While cranking engine there should be no fuel spray with injector disconnected. Replace injector if it sprays or if it drips.
4. If injector is okay, fuel system appears to be operating normally. Using ST125 spark gap tool, check voltage at spark plugs. No spark indicates an HEI problem. If spark is satisfactory, check the following; Throttle Position Sensor (TPS) for sticking or binding in wide open throttle position, coolant sensor "OPEN" signal to ECM using Code 15 chart, check for ice (cold weather) or foreign material in fuel. Engine may start after 5-6 minutes in heated shop. Check for EGR sticking open, open crank signal (cold weather), low fuel pressure or volume (lean air/fuel ratio). See A5.
5. The EFI system is considered okay if no trouble was found. Reconnect injector and look for possible mechanical problems.
6. No spray from injector indicates a faulty fuel system or no ECM control of injector. If test light "blinks" while cranking, ECM control is considered okay. Light may dim while "blinking". Use bulb 1847 or equivalent.

Flow Chart A3: Cranks But Won't Run (All). Scheme 714

Flow Chart A3: Cranks But Won't Run (All). Scheme 715

Chart A3 Schematic: Cranks But Won't Run (All). Scheme 716

CHART A4 - CRANKS BUT WON'T RUN (A/F/J/N/P BODY)

1. Circuit No. 439 supplies ignition voltage to injector. Using a test lamp, probe each connector terminal. Test lamp should light on one (1) terminal, confirming voltage at connector. The ECM injector circuit No. 467 may be open. Reconnect injector. Using test lamp, probe terminal 8 of White ECM connector. A light at this point indicates that injector drive circuit is okay.
2. No "blinking" light indicates no ECM control of injector. With voltmeter on AC 2 volt range, voltage should be greater than .7 volts. If voltage is less than .7 volts, there is an open or short to ground in HEI reference circuit No. 430. If circuit is okay, there is an HEI problem. 8A) Disconnect distributor connector. Momentarily touch ECM side of connector, circuit No. 430, with a test lamp connected to 12 volts. Note injector as contact is made. Injector should turn on. If injector turns on, ECM circuit is okay. Connect spark tool ST125 and check for spark. If spark is okay, HEI module is faulty. No spark indicates an HEI problem.

Flow Chart A4: Cranks But Won't Run (All). Scheme 717

Flow Chart A4: Cranks But Won't Run (All). Scheme 718

CHART A5 - FUEL SYSTEM DIAGNOSIS (A/F/J/N/P BODY)

The ECM turns iNtank fuel pump on as long as ignition is on and the engine is cranking or running. The ECM will allow the pump to run as long as it receives reference pulses from distributor. If there are no reference pulses, the ECM will shut off the fuel pump within 2 seconds after key is in "ON" position. The fuel pump test terminal is located on left side of engine compartment. When engine is stopped, pump can be turned on by applying battery voltage to test terminal. Improper fuel system pressure will result in one (1) or all of the following symptoms: cranks but will not run, Code 44, Code 45, engine cuts out (may feel like ignition problem), poor fuel economy, loss of power and hesitation.

1. If the fuse is blown, this test will confirm a short to ground on circuit No. 120. To prevent miSdiagnosis, be sure fuel pump is disconnected before test.
2. This test determines if pump circuit is ECM controlled. The ECM will turn pump relay on, then turn it off after 2 seconds, if engine is not cranking or running.
3. This step turns fuel pump on, if circuit No. 120 wiring is okay.
4. This step checks for battery voltage at fuel pump relay.

Flow Chart A5: Fuel System Diagnosis. Scheme 719

Flow Chart A5: Fuel System Diagnosis (1 Of 2). Scheme 720

Flow Chart A5: Fuel System Diagnosis (2 Of 2). Scheme 721

Chart A5 Schematic: Fuel System Diagnosis. Scheme 722

CHART A6 - FUEL SYSTEM DIAGNOSIS (A/F/J/N/P BODY)

Note. Continued from CHART A5.

1. This step checks relay ground circuit No. 450.
2. This step checks ECM control of relay through circuit No. 465.
3. The fuel pump circuit includes an engine oil pressure switch. If fuel pump relay fails, the fuel pump will continue to run via oil pressure switch circuit. Relay failure will result in extended cranking times and possible no start condition.
4. This test checks the oil pressure switch to be sure it provides battery feed to fuel pump if pump relay fails.
5. This test checks for open oil pressure switch with ignition off. Should switch stick closed, fuel pump will continue to run and discharge battery.

Flow Chart A6: Fuel System Diagnosis. Scheme 723

Flow Chart A6: Fuel System Diagnosis. Scheme 724

CHART A7 - FUEL SYSTEM DIAGNOSIS (A/F/N/P BODY)

Note. Continued from CHART A5.

1. Pressure below 9 psi falls into 2 categories: If regulated pressure is less than 9 psi and volume to injector is adequate, system will run lean and cause Code 44. Engine will be hard to start when cold and have poor overall performance. A restricted fuel flow is causing pressure drop. Normally, a vehicle with fuel pressure of less than 9 psi at idle will not be driveable. However, if pressure drop occurs only when driving, the engine will surge then stop as pressure begins to drop.
2. Restricting the fuel return line allows the fuel pump to develop its maximum pressure. When battery voltage is applied to pump test terminal, pressure should be between 13 to 18 psi.
3. This test determines if high fuel pressure is due to a restricted fuel return line or a throttle body pressure regulator problem.

Flow Chart A7: Fuel System Diagnosis. Scheme 725

Flow Chart A7: Fuel System Diagnosis. Scheme 726

Component Locations (A/N Body 2.5L). Scheme 727

Component Locations (F/P Body 2.5L). Scheme 728

ECM Terminal ID & Pin Voltage (A/F/N Body 2.5L). Scheme 729

ECM Terminal ID & Pin Voltage (P Body 2.5L). Scheme 730

CCC Wiring Diagram. Scheme 731