2.3l Pfi Tests W/codes Buick Skylark VI

DIAGNOSTIC CIRCUIT CHECK

The Diagnostic Circuit Check is an organized approach to identifying computer controlled system malfunction. It is the starting point in which system diagnosis should begin.

Note. Any "Scan" tester that displays faulty data should not be used. The use of such a "Scan" tester can result in misdiagnosis and unnecessary component replacement.

In order to verify proper "Scan" tester operation and/or correct ECM data, the ALDL test connector should be grounded with ignition key on, check for a Code 12. See CHART A-2.

Diagnostic Circuit Check - Flow Chart. Scheme 293

CHART A-1: NO "SERVICE ENGINE SOON" LIGHT

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

1. If fusible link is blown, locate and repair short to ground.
2. With test light connected to battery voltage, probe each system ground circuit to ensure that ground is present. See ECM TERMINAL IDENTIFICATION chart under «PIN VOLTAGE CHARTS»(/buick/skylark/vi-1986-1992/remont/testing-diagnostics/#23l-pfi-tests-wcodes__pin-voltage-charts) at end of article, for pin locations of ground circuits.

Diagnostic Aids

If engine runs okay, check for the following conditions

1. Faulty light bulb.
2. Open circuit No. 419.
3. Blown instrument panel fuse. This will result in loss of "SERVICE ENGINE SOON" (SES) light, oil pressure light and brake light.

Engine cranks but will not run. Check for

1. Fusible link open (continuous battery voltage).
2. Open ECM ignition fuse.
3. Open circuit No. 2 (battery voltage) to ECM.
4. Open ignition circuit No. 439 to ECM.
5. Improper connection to ECM.
6. Improper ECM ground.

Chart A-1 Schematic, No "SES" Light. Scheme 294

Chart A-1, No "SES" Light. Scheme 295

CHART A-2, NO ALDL DATA OR WON'T FLASH CODE 12 "SERVICE ENGINE SOON" (SES) LIGHT "ON" STEADY

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

1. Light off, with circuit No. 419 disconnected from ECM, indicates that ground circuit was completed through ECM, not through external short to ground.
2. If a problem exists with ECM that does not allow "Scan" tester to read serial data, ECM should not flash Code 12. If Code 12 is present, check circuit No. 451 for short to ground. If Code 12 is not present, ensure that "Scan" tester is functioning properly by testing on another vehicle. If "Scan" tester is functioning properly and circuit No. 461 is okay, MEM-CAL or ECM may be at fault, when no ALDL data condition exists.
3. This step will check for an open diagnostic circuit No. 451.
4. SES light circuit is okay, and problem is faulty ECM or MEM-CAL. If Code 12 is present, ECM should be replaced using the original MEM-CAL. Replace MEM-CAL only after replacing ECM, as MEM-CAL is not likely to be at fault.

Chart A-2, No ALDL Data or No Code 12 "SES" On Steady. Scheme 296

CHART A-3, ENGINE CRANKS BUT WON'T RUN

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

1. Verifies that SES light operation, on-board diagnostics, cranking RPM, TPS and coolant sensor signals are normal. Flashing test light verifies that ECM is receiving IDI reference signal and attempting to activate injectors.
2. This step assists in checking for opens or shorts to injectors and injector harness. Resistance should measure half that of one injector due to parallel circuit.
3. This step checks for each ignition coil's ability to produce at least 25,000 volts. This is accomplished by installing spark plug jumper leads and testing for spark at 2 adjacent plug leads. DO NOT use plugs No. 2 and 3 as they are controlled through same coil.
4. Correct operation of fuel pump and relay are verified. Fuel pump should only operate for 2-3 seconds and fuel pressure should be within specification range.
5. A blinking test light indicates that fault is within coil harness or connections. If test light does not blink, module or its connections are faulty.
6. Injector nominal resistance is 1.9-2.1 ohms at 140°F (60°C). Resistance will increase at higher temperatures. This test will determine whether harness or injector is cause of incorrect resistance values.

Check for the following

1. Intermittently shorted or opened TPS circuit, or TPS binding or sticking in WOT position.
2. Contaminated fuel or water in fuel system.
3. Timing chain failure or low compression.
4. Check that only resistor spark plugs are used.

Chart A-3 Schematic, Cranks But Won't Run. Scheme 297

Chart A-3 (1 of 3), Cranks But Won't Run. Scheme 298

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

Scheme 299

1. 7) Cavity "A" should have battery voltage whenever fuel pump power feed circuit is switched on. ECM activates fuel pump for 2-3 seconds after ignition is turned on, and when ignition references pulses are being received during cranking and engine running. Ignition should be turned off at least 10 seconds to ensure that ECM powers down. After ECM powers down, it will then reactivate fuel pump for 2-3 seconds when ignition is turned on.
2. 8) Illumination of light on one circuit indicates power is available at cavity "A" only, but grounded circuit is not being completed on other circuit. This condition may exist due to an open circuit, or ECM failing to switch injector driver circuit to ground.
3. 9) Constant light indicates ground circuit is always closed and is not being switched. This may be due to a short to ground, or faulty ECM injector driver.
4. 10) Fuel pump is energized by ECM for 2-3 seconds after ignition is first turned on. If engine is not started, it is necessary to turn ignition off for at least 10 seconds to ensure that ECM powers down. If power is not available at injectors and fuel pump operates, an open circuit exists. If fuel pump fails to operate, refer to CHART A-5 for diagnosis. (Scheme 299): Chart A-3 (2 of 3), Cranks But Won't Run NOTE: Test numbers refer to test numbers on diagnostic chart.
5. 11) Terminal "K" should provide good ground, while terminal "L" of IDI 11-pin connector, should provide battery voltage.
6. 12) Test light to 12 volts simulates reference signal to ECM. If circuit No. 430, ECM and injector driver circuit are operating properly, test light should flash.
7. 13) Output voltage should be present at crankshaft sensor as crankshaft rotates. If output voltage is not present, faulty sensor connection or sensor is indicated.
8. 14) Crank sensor's core is magnetized. Resistance should be within 500-900 ohm range.

Chart A-3 (3 of 3), Cranks But Won't Run. Scheme 300

CHART A-5, CRANKS BUT WON'T RUN (FUEL PUMP CIRCUIT)

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

Scheme 301

Scheme 302

1. This will determine if ECM is controlling fuel pump circuit. ECM turns on fuel pump relay. When engine is not being cranked or engine is running, ECM will turn off relay within 2 seconds after ignition is turned on.
2. If fuse is blown, this test will confirm a short to ground on circuit No. 120. To prevent misdiagnosis, ensure fuel pump is disconnected before test.
3. Activates fuel pump if circuit No. 120 is okay. If pump operates, it is a basic fuel delivery problem which the following steps will locate.
4. Check for battery voltage at pump relay. (Scheme 301): Chart A-5 Schematic, Cranks But Won't Run (Fuel Pump Ckt) (Scheme 302): Chart A-5 (1 of 2), Cranks But Won't Run (Fuel Pump Ckt) NOTE: Test numbers refer to test numbers on diagnostic chart.
5. Check relay ground circuit No. 450.
6. Check for ECM control of relay through circuit No. 465.
7. An engine oil pressure switch with separate set of normally open contacts is included in fuel pump voltage control circuit. At 4 psi (.28 kg/cm 2 ) of oil pressure, switch should close and provide second voltage feed path to fuel pump. If relay fails, pump will continue to run using voltage supplied through closed oil pressure switch. A failed fuel pump relay usually results in extended engine cranking time needed to start engine. This is due to time required to build enough oil pressure to close contacts. If cranking speed is not sufficient, engine may not start. If oil pressure switch is faulty engine may not start.
8. Ensure that oil pressure switch provides battery voltage to fuel pump, in the event fuel pump relay fails.

Chart A-5 (2 of 2), Cranks But Won't Run (Fuel Pump Ckt). Scheme 303

CHART A-7, FUEL SYSTEM DIAGNOSIS

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

Scheme 304

Scheme 305

1. Use shop towel to soak up excess fuel spillage that may occur when installing pressure gauge. With ignition on, pump pressure should be 40-47 psi (2.8-3.3 kg/cm 2 ). Pressure is controlled by pressure regulator on fuel rail.
2. During engine idle, manifold vacuum is applied to regulator diaphragm. Vacuum offsets spring pressure and results in lower fuel pressure. Idle pressure should vary depending on barometric pressure (or manifold vacuum). Idle fuel pressure should be lower than higher RPM pressure, indicating regulator control.
3. Rapidly falling pressure is caused by one of following: Check valve not holding on in-tank fuel pump. Pump pulsator or coupling leaking. Pressure regulator valve leaking. Injector(s) sticking open.
4. An injector sticking or open can best be determined by checking for a fouled or saturated spark plug(s). If a leaking injector can not be determined by using this method, the following procedure should be used: Remove plenum and fuel rail bolts. See appropriate article in FUEL SYSTEMS section. Fuel lines should remain connected. Fuel rail should be lifted out just enough to leave injector nozzles in ports. CAUTION: To prevent possible engine fire, ensure that injectors are not allowed to spray on engine. Also, check that injector retaining clips are intact. After pressurizing fuel system, check for leaking injector(s). (Scheme 304): Chart A-7 Schematic, Fuel System Diagnosis (Scheme 305): Chart A-7 (1 of 2), Fuel System Diagnosis NOTE: Test numbers refer to test numbers on diagnostic chart.
5. If pressure is less than specifications, lean condition or Code 44 may be set. Hard cold start or poor driveability may result from this condition. Low or restricted fuel pressure may cause intermittent engine stall and/or surge or stall during load conditions, as when accelerating or driving at high speeds.
6. Restricting fuel line allows fuel pump to operate at maximum pressure (dead head pressure). Pump pressure should be greater than 61 psi (4.3 kg/cm 2 ) when battery voltage is applied to pump test terminal.
7. This test will determine whether a restricted fuel return line or faulty pressure regulator, is cause of high fuel pressure. High fuel pressure may set a Code 45 or cause driveability problems.

Chart A-7 (2 of 2), Fuel System Diagnosis. Scheme 306

CHART B-1, RESTRICTED EXHAUST SYSTEM CHECK

Before any components are replaced, exhaust system must be checked for restrictions.

Check at O2 Sensor

Remove O2 sensor. Install backpressure tester in place of O2 sensor as shown in illustration. After test is completed, ensure that O2 sensor threads are coated with anti-seize compound before installation.

Diagnosis

1. Start engine and bring to operating temperature. Allow engine to idle and observe exhaust system backpressure gauge. Reading should not exceed .5 psi (.04 kg/cm 2 ).
2. Increase engine speed to 3000 RPM and note gauge. Reading should not exceed .75 psi (.05 kg/cm 2 ).
3. If during steps 1) or 2), specification is exceeded, exhaust system restriction is indicated.
4. Check complete exhaust system for collapsed pipe, heat distress and possible internal muffler failure.
5. If none of the conditions in step 4) exist, check for restricted catalytic converter. Replace if necessary.

Chart B-1, Installing backpressure Tester. Scheme 307

CODE 13, OPEN OXYGEN SENSOR CIRCUIT

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

1. The following conditions must exist to set a Code 13: Engine running at least 40 seconds after start. Engine coolant temperature greater than 108.5°F (42.5°C). Code 21 or 22 must not be set. Oxygen sensor voltage steady between .34 and .55 volt. TPS signal greater than 6 percent for more time than less than 6 percent, or about .3 volt greater than closed throttle voltage. Conditions must be met and held for at least 20 seconds.
2. This test will indicate whether sensor is faulty, or if wiring and/or ECM is cause of Code 13. NOTE: Use only high impedance digital volt/ohmmeter for this test.
3. This test checks for continuity of circuits No. 412 and 413. If circuit No. 413 is open, ECM voltage on circuit No. 412 will be greater than .6 volt (600mV).

Normal scan voltage ranges between .1-1.0 volt (100-999 mV), while in "closed loop". Code 13 will set in 20 seconds if voltage remains between .35-.55 volt. System will go into "open loop" in about 15 seconds. See INTERMITTENTS in CCC EFI TESTS W/O CODES .

Code 13 Schematic, Open O2 Sensor. Scheme 308

Code 13 Flow Chart, Open O2 Sensor Circuit. Scheme 309

CODE 14, COOLANT TEMP SENSOR SIGNAL VOLT LOW

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

1. Code 14 will be set if signal voltage indicates temperature greater than 285°F (140°C) and engine has been operating for more than 128 seconds.
2. This test will indicate if circuit No. 410 is shorted to ground and set a code 14.

After engine is started, temperature should rise steadily to about 90°F (32°C), then stabilize when thermostat opens.

If the engine is allowed to cool overnight, the coolant and MAT sensors, when measured with a "Scan" tester, should read close to each other. When Code 14 is set, ECM will turn on the cooling fan. The Temperature vs Resistance Values table (scale) may be used to test the coolant temperature sensor at various temperature levels. This enables an evaluation of a possible "shifted" (mis-scaled) sensor. A shifted sensor could result in poor driveability complaints.

Code 14 Schematic, Coolant Temp Sensor Signal Volt Low. Scheme 310

Code 14 Flow Chart, Coolant Temp Sensor Signal Volt Low. Scheme 311

CODE 15, COOLANT TEMP SENSOR SIGNAL VOLT HIGH

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

1. Code 15 will set if signal voltage indicates a coolant temperature less than -40°F (-40°C) for 60 seconds.
2. This test simulates conditions for a Code 14. If ECM recognizes low signal voltage and "Scan" tester indicates 130°C, ECM and wiring are okay.
3. This test will determine if circuit No. 410 is open. Five volts should be present at sensor connector if measured with DVOM.

After engine is started, temperature displayed by "Scan" tester should rise steadily to about 95°C, then stabilize when thermostat opens. It is normal for coolant temperature to fluctuate slightly around 95°C. Faulty connection or an open in circuit No. 410 or No. 452, can result in a Code 15. Codes 15, 21 and 66 stored at the same time could be result of an open circuit No. 452.

Code 15 Flow Chart, Coolant Temp Sensor Signal Volt Hi. Scheme 312

CODE 21, TPS SIGNAL VOLTAGE HIGH

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

1. The following conditions must be met to set a Code 21: Engine running at operating temperature. No Codes 33 or 34. MAP less than 65 kPa. TPS signal voltage greater than about 4 volts (78 percent). Above conditions must exist for more than 5 seconds, or TPS voltage greater than about 4.7 volts.
2. With TPS unplugged, voltage should reduce to a lower value, if ECM and wiring are okay.
3. Probing circuit No. 452 using a test light, checks TPS ground circuit. An open or very high resistance ground will set a Code 21.

When using a "Scan" tester, throttle position should be displayed in voltage. Check TPS voltage with ignition on and engine off. At closed throttle display should read .49-.59 volts. Voltage should increase at a steady rate as throttle is opened toward WOT position. Some scan tools will display throttle angle in percentages (0 percent=closed throttle and 100 percent=WOT). An open circuit No. 452 will set a Code 21. Codes 15, 21 and 66 stored simultaneously could be result of an open circuit No. 452. Check TPS connector for corrosion or improper connection. Check condition of connector seal and replace if necessary.

Code 21 Schematic, TPS Signal Volt Hi. Scheme 313

Code 21 Flow Chart, TPS Signal Volt Hi. Scheme 314

CODE 22, TPS SIGNAL VOLT LOW

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

1. In order for Code 22 to set, engine must be running and TPS signal voltage should be less than about .2 volt for 3 seconds.
2. This test simulates high voltage (Code 21). If ECM recognizes high signal voltage, ECM and wiring are okay.
3. TPS has an auto zeroing feature. If voltage is within range of .4-.9 volt, ECM will use that value as closed throttle. If voltage reading is out of zeroing range, TPS must be replaced.
4. A high voltage signal is simulated to check for an open in circuit No. 417.

When using a "Scan" tester, throttle position should be displayed in voltage. Check TPS voltage with ignition on and engine off. At closed throttle, display should read .49-.59 volt. Voltage should increase at a steady rate as throttle is opened toward WOT position. Some scan tools will display in percentages (0 percent = closed throttle and 100 percent=WOT). Codes 22, 33 and 66 stored simultaneously could be result of an open circuit No. 416. Check TPS connector for corrosion or improper connection. Check condition of connector seal, replace if necessary.

Code 22 Flow Chart, TPS Signal Volt Low. Scheme 315

CODE 23, MAT SENSOR SIGNAL VOLT HI

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

1. The following conditions must exist for a Code 23 to set: Signal voltage indicates manifold air temperature is less than -29°F (-34°C). Engine has been running for at least 320 seconds. Vehicle speed is less than 15 MPH.
2. Code 23 is set due to an open sensor, wire or connection. This test determines if wiring and ECM are okay.
3. This test indicates if signal circuit No. 472 or 5-volt return circuit No. 469 is open.

"Scan" tester should display temperature of air entering engine close to ambient air temperature when engine is cold, and rise as underhood temperature increases. Improper connections or open circuits No. 472 or 469, can set Code 23. Codes 23 and 24 stored simultaneously, could be result of an open circuit No. 469.

Code 23 Schematic, MAT Sensor Signal Volt Hi. Scheme 316

Code 23 Flow Chart, MAT Sensor Signal Volt Hi. Scheme 317

CODE 24, VEHICLE SPEED SENSOR (VSS) CIRCUIT

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

1. Code 24 will set (with vehicle speed less than 2 mph) only if the following conditions are met: Engine RPM is between 1600 and 3600. TPS is greater than 7 percent. Gear selector not in Park or Neutral. All conditions met for 20 seconds. No Codes 21 or 22. Above conditions are met during road load deceleration. Ignore Code 24 that sets when drive wheels are turning faster than 3 MPH. PM generator only produces a signal if drive wheels are turning greater than 3 mph.
2. Ensure that correct PROM is used before replacing ECM.

A problem in circuit No. 434 will not affect VSS input or readings displayed by "Scan" tester. Ensure that circuits No. 400 and 401 have proper connections. Also check for correct harness routing.

Note. On vehicles with automatic transmission, a faulty or improperly adjusted park/neutral switch can result in a false Code 24. Use a "Scan" tester and check for proper signal while in Drive. Refer to CHART C-1A for P/N switch diagnosis.

Code 24 Schematic, VSS Circuit. Scheme 318

Code 24 Flow Chart, VSS Circuit. Scheme 319

CODE 25, MAT SENSOR SIGNAL VOLT LOW

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

1. Code 25 will set only if signal voltage indicates manifold air temperature greater than about 318°F (159°C) and if vehicle speed is greater than 15 MPH.

Use temperature scale to check MAT resistances. This scale should be used to eliminate the possibility of a mis-scaled sensor. A mis-scaled sensor could be the cause of poor driveability.

Code 25 Flow Chart, MAT Sensor Signal Volt Lo. Scheme 320

CODE 26, QUAD-DRIVER ERROR

The ECM controls most components with electronic switches that complete a ground circuit when actuated. These switches are arranged in groups of 4, called Quad-Driver Modules (QDM's), which can independently control up to 4 outputs (ECM terminals). When an output is actuated, the terminal is grounded and its voltage normally will be low. When an output is off, its terminal voltage normally will be high, except for the TCC, which depends on the brake and 2nd gear TCC switches.

QDM's are fault protected. If a relay or solenoid coil is shorted, having very low resistance, or if control side of circuit is shorted to voltage, it would allow too much current into QDM. The QDM senses this and turns the output off, or its internal resistance increases to limit current flow and protect the QDM. The result is high output terminal voltage when it should be low. If the circuit from battery voltage or the component is open, or the control side of circuit is shorted to ground, terminal voltage will be low, even when output is turned off. Either of these conditions is considered to be a QDM fault.

Each QDM has a separate fault line to indicate the presence of a current fault to ECM's central processor. A "Scan" tester displays the status of each of these fault lines as "low equals okay" or "high equals fault". Because of the brake and 2nd gear switches in the TCC circuit, Code 26 is set under different conditions for QDM A and QDM B. Those conditions are as described

1. QDM A fault line equals "high" for 20 seconds or more.
2. QDM B fault line equals "high" for 20 seconds or more, and brake switch signal indicates brake switch is closed and 2nd gear state switch indicates transaxle is in 2nd or 3rd gear, or TCC is commanded on.

Note. QDM B fault line on an automatic transaxle vehicle will normally be "high" when the vehicle is stopped. The ECM ignores the QDM B fault line except under conditions noted above.

Code 26 Schematic, Quad-Driver Error. Scheme 321

Code 26 Flow Chart (1 of 3), Quad-Driver Error. Scheme 322

Code 26 Schematic (2 of 3), Quad-Driver Error. Scheme 323

Code 26 Flow Chart (2 of 3), Quad-Driver Error. Scheme 324

Intermittent faults must be continuously present for at least 20 seconds to cause Code 26 to set. QDM controlled circuits should be inspected for poor terminal contact or damaged harness. The TCC circuit should be checked with the transaxle at operating temperature if Code 26 sets intermittently and no other cause is found, as a defective TCC solenoid resistance can drop too low (below 20 ohms) at high temperature. QDM faults can be detected as noted on CODE 26 chart (Page 1 of 3) and when outputs are on or off as follows

1. Open circuit or control circuit short to ground-output commanded off.
2. Shorted device or control circuit short to voltage-output commanded on.

Note. QDM B fault line on an automatic transaxle vehicle will normally be "high" when the vehicle is stopped. The ECM ignores the QDM B fault line except under conditions noted above.

Code 26 Flow Chart (3 of 3), Quad-Driver Error. Scheme 325

CODE 33, MAP SENSOR SIGNAL VOLT HI

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

1. The following conditions must be met to set a Code 33: MAP signal greater than 80 kPa. TPS reading below 12 percent. VSS reading below one MPH. Above conditions met for 5 seconds.
2. With MAP sensor unplugged, ECM terminal "YD15" voltage should be low if ECM and wiring are okay.

An intermittent open in circuit No. 469 can result in Code 33.

Code 33 Schematic, MAP Sensor Signal Volt Hi. Scheme 326

Code 33 Flow Chart, MAP Sensor Signal Volt Hi. Scheme 327

CODE 34, MAP SENSOR SIGNAL VOLT LO

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

1. The following conditions must be met to set a Code 34: Engine running at operating temperature. No Code 21. MAP reading less than 14 kPa. Engine RPM less than 1200 or TPS greater than 15.2 percent. Above conditions met for 2 seconds.
2. This test checks for sensor being at fault for low voltage, or if there is an ECM or wiring problem.
3. This test simulates high signal voltage to check for open in circuit No. 432. If test light is bright during this test, circuit No. 432 is probably shorted to ground. If "Scan" tester reads greater than 4 volts at this test, circuit No. 416 can be checked by measuring voltage at terminal "C". Reading should be 5 volts.

An intermittent on circuit No. 416 or 469, will result in a Code 34.

Code 34 Flow Chart, MAP Sensor Signal Volt Lo. Scheme 328

CODE 35, IAC IDLE SPEED ERROR

This code is intended to detect intake vacuum leaks. The following conditions must be met to set a Code 35

1. Engine speed at least 175 RPM greater or less than specification.
2. TPS signal voltage indicates throttle position less than one percent.
3. VSS indicates vehicle speed is less than 3 MPH.
4. Above conditions are met for 5 seconds or longer.

Always check for vacuum leaks, disconnected lines, brittle hoses, cuts, improper connections, etc. Check throttle body and manifold gaskets for proper seal. Also check for cracked intake manifold. Ensure that TPS and MAP sensor are operating properly. Compare to a known good vehicle if necessary. Check for possible open in circuits No. 441, 442, 443 and 444, or faulty connections at ECM terminals "YE3", "YE4", "YE5" and "YE6". An open, short or poor connection in any of the mentioned circuits will result in improper idle control and may cause a Code 35. If IAC valve is stopped in an open position and can't respond to ECM, or minimum air rate throttle stop screw is set too high, Code 35 could result. If no problem is found and Code 35 resets, replace ECM.

Code 35 Flow Chart, IAC Idle Speed Error. Scheme 329

CODE 41, 1X REFERENCE CIRCUIT

The ignition module sends a signal to the ECM once per revolution to indicate crankshaft position. The ECM uses this information to determine when to pulse injectors for cylinders No. 2 and 3. This signal can be described as a synchronization signal and is called 1X reference because it occurs one time per revolution. The ignition module applies 5 volts from terminal "G" through circuit No. 969 to ECM terminal "BC5" and in effect, switches this circuit to ground for a short period of time, 125 degrees before TDC of cylinders No. 2 and 3. Code 41 is set if ECM receives (8) 2X reference pulses with no 1X reference pulses. When Code 41 is present, ECM pulses injectors in the simultaneously mode.

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

1. This determines if ECM recognizes a fault. If a Code 41 is not set at this point, problem is intermittent and could be the result of a loose connection.
2. This step simulates 1X signal. ECM should recognize the drop in voltage as test light probe is removed, if circuit and ECM are okay. This step will also give accurate results only if chart sequence is used (ignition off or ignition on), "Scan" tester set to 1X reference and terminal "G" contacted using test light probe.
3. If ECM did not recognize simulation of 1X signal, circuit No. 969 may be open or shorted to ground or voltage. If circuit No. 969 is okay, ECM is faulty.
4. Step 2 indicated that circuit No. 969 is okay and ECM is capable of recognizing simulated 1X reference pulse. This indicates either a poor connection at ignition module terminal "G", or a faulty ignition module caused Code 41 to occur.

An intermittent may be caused by a poor connection, rubbed through wire insulation, or a wire broken inside the insulation. Inspect ECM harness connector terminal "BC5" and ignition module terminal "G" for improperly formed or damaged terminals, poor terminal to wire connection and damaged harness.

Code 41 Flow Chart, 1X Reference Circuit. Scheme 330

CODE 42, EST CIRCUIT OPEN OR GROUNDED

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

1. Checks to see if ECM recognizes a fault. If a Code 42 is not set at this point, an intermittent problem exists and could be the result of a loose connection.
2. With ECM disconnected, ohmmeter should indicate less than 500 ohms, which is normal resistance for the ignition module. A higher resistance indicates a fault in circuit No. 423, poor ignition module connection or faulty ignition module.
3. If test light was illuminated when connected from 12 volts to ECM harness terminal "BC7", either circuit No. 423 is shorted to ground or ignition module is faulty.
4. Checks to see if ignition module switches when bypass circuit is energized by 12 volts through test light. If ignition module switches, ohmmeter reading should shift to greater than 8000 ohms.
5. Disconnecting ignition module should cause ohmmeter to indicate as if it were monitoring an open circuit (infinite reading). If ohmmeter has a reading other than infinity, circuit No. 423 is shorted to ground.

An intermittent may be caused by a poor connection, rubbed through wire insulation or wire broken inside insulation. Inspect ECM harness connectors for backed out terminals "BC7" or "BC8", improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection and damaged harness.

Code 42 Flow Chart, EST Circuit Open or Grounded. Scheme 331

CODE 43, ELECTRONIC SPARK CONTROL

Code 43 indicates the ECM has seen high or low voltage at circuit No. 496 for longer than 5 seconds with the engine running.

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

1. If conditions for test as described above are being met, Code 43 will currently set and the "SES" light will be illuminated.
2. The ECM has a 5-volt pull-up resistor, which should be present at the knock sensor terminal.
3. This test determines if internal resistance of knock sensor is within an acceptable range.

Check circuit No. 496 for a potential short or open to ground. Also check for proper installation of MEM-CAL. Mechanical engine knock can cause a knock sensor signal. Abnormal engine noise must be corrected before using this chart.

Note. Code 43 circuit diagram and flow chart has been updated by Technical Service Bulletin No. 91-6-6, dated 8/24/90 for Pontiac models, Technical Service Bulletin No. 91-6E-01, dated 8/24/90 for Buick models and Technical Service Bulletin No. 91-T-07, dated 8/24/90 for Buick models.

Code 43 Schematic, Electronic Spark Control. Scheme 332

Code 43 Flow Chart, Electronic Spark Control. Scheme 333

CODE 44, LEAN EXHAUST INDICATED

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

1. The following conditions must be met to set a Code 44 when signal voltage is present on circuit No. 412: Value remains below .3 volt for 50 seconds or more. System is operating in "closed loop". No Code 33 or 34. "Closed loop" integrator active.

Code 44 or lean exhaust is most likely caused by one of following

1. Fuel Pressure - System will be lean if pressure is too low. It may be necessary to monitor fuel pressure while driving vehicle at various road speeds and/or loads to confirm condition. Refer to CHART A-7 for further diagnosis.
2. MAP Sensor - An output that causes ECM to sense a lower than normal manifold pressure (high vacuum) can cause system to operate lean. Disconnecting MAP sensor will allow ECM to substitute a fixed (default) value for MAP sensor. If rich condition discontinues when sensor is disconnected, substitute using a known good sensor and recheck.
3. Fuel Contamination - Water, even in small amounts, near in-tank fuel pump inlet can be delivered to injector(s). Water delivered to injector(s) causes lean exhaust and may set a Code 44.
4. Sensor Harness - Sensor pigtail may be mispositioned and+ contacting exhaust manifold.
5. Engine Misfire - A cylinder misfire will result in unburned fuel mixture in the exhaust, which may set a Code 44. Refer to CHART C-4M and/or SYMPTOMS in THEORY & OPERATION.

Code 44 Flow Chart, Lean Exhaust Indicated. Scheme 334

CODE 45, RICH EXHAUST INDICATED

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

1. The following conditions must be met to set a Code 45: O2 sensor voltage is greater than .75 volt. No Code 33 or 34. Fuel system in "closed loop". TPS greater than 5 percent. Above conditions met for 50 seconds.

Code 45 or rich exhaust is most likely cause by one or a combination of the following conditions

1. Fuel Pressure - Engine will operate in a rich condition if fuel pressure is to high. ECM can compensate for some increase. If increase is greater than a certain value a Code 45 will be set. For fuel system diagnosis see CHART A-7.
2. Leaking Injectors - Check for leaking injector(s). See CHART A-7.
3. HEI Shielding - Check Integrated Direct Ignition (IDI) shielding. An open ground circuit No. 453 may result in induced electrical noise. The ECM may see this noise as distributor pulses and richen mixture. Engine tachometer will indicate a higher than actual engine speed, which can aid in diagnosing problem.
4. Canister Purge - Check canister purge for fuel saturation. If fuel saturation is present, check control and hoses. See appropriate article in FUEL SYSTEMS section.
5. Map Sensor - An output from the MAP sensor that is higher than normal (low vacuum) can cause ECM to richen mixture. Unplugging MAP sensor will allow ECM to set a fixed value for MAP sensor. Check for cracked or punctured hose. Replace MAP sensor with a known good sensor and check for rich condition. If condition disappears, replace MAP sensor.
6. Pressure Regulator - Check pressure regulator for lack of pressure retention. Check diaphragm by inspecting vacuum line for liquid (raw) fuel.
7. TPS - An intermittent TPS output can cause a rich condition. This is due to false indication of engine being accelerated.
8. Oxygen Sensor Contamination - Check O2 sensor for contamination from fuel or use of improper LTV sealant. O2 sensor may have White powdery coating and result in a high, but false signal voltage (rich indication). ECM will then reduce fuel delivery to engine causing a severe surge driveability problem.

Code 45 Flow Chart, Rich Exhaust Indicated. Scheme 335

CODE 51, FAULTY MEM-CAL

This code indicates a faulty or incorrect MEM-CAL. Ensure that all pins are properly inserted in socket and that MEM-CAL is correctly latched. If okay, replace MEM-CAL, clear memory and recheck. If Code 51 reappears, replace ECM.

Note. To prevent possible electrostatic discharge damage to the ECM or MEM-CAL, do not touch the component leads, and do not remove the integrated circuit from carrier.

CODE 53, FAULTY ALTERNATOR, VOLT HIGH

If ECM terminals "BB1" and "BC16" voltages are more than 17.1 volts for about .2 second, with ignition on, a Code 53 will be set. During this time when failure is present, all ECM outputs will be disengaged. Additional codes may result.

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

1. Battery output should be between 10-17 volts.
2. This test checks to see if voltage reading is due to generator or ECM. With engine running, check battery voltage. If reading is greater than 17.1 volts, ECM is okay.
3. This step checks for faulty generator under load condition. If voltage is greater than 17.1 volts, see alternator diagnosis in appropriate article in ELECTRICAL section.

Code 53 Schematic, Faulty Alternator, Volt Hi. Scheme 336

Code 53 Flow Chart, Faulty Alternator, Volt Hi. Scheme 337

CODE 62, GEAR SWITCH ERROR

Code 62 is used to check 2nd and 3rd gear switch inputs to ECM. In order to determine transmission gear input signals to ECM, see INPUT SIGNALS table.

INPUT SIGNALS

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

1. If the following conditions are met for about 17 seconds, a Code 62 will be set: In Park or Neutral and 2nd or 3rd gear indicated. Vehicle speed less than about 5 MPH, and 2nd or 3rd gear indicated. First or 2nd gear indicated. Less than about 3000 RPM. Gear selector not in Park or Neutral, and VSS greater than 50 MPH. First step checks for an open or grounded circuit between transmission connector and ECM. Since ECM terminals are normally high, battery voltage should be indicated at both terminals with connector removed.
2. Digital voltmeter should measure zero volt at terminal "B" because 3rd gear switch should be open, providing no continuity to ground. Terminal "C" should measure near battery voltage because 2nd gear switch should provide continuity to ground.
3. This test checks for normally functioning transmission switches. In 3rd gear both switches should have changed from their original 1st gear state.

Clear codes and recheck for Code 62. If code resets, check all harness connections, VSS, RPM, P/N circuits prior to replacing ECM. Transmission starting in 2nd or 3rd gear can also set a Code 62

Code 62 Schematic, Gear Switch Error. Scheme 338

Code 62 Flow Chart, Gear Switch Error. Scheme 339

CODE 65, FUEL INJECTOR CURRENT LOW

The ECM has 2 injector driver circuits, each of which controls a pair of injectors (1 and 4, or 2 and 3). The ECM monitors current of each injector driver circuit by measuring voltage drop through a fixed resistor. The ECM is able to control voltage drop. The current through each driver is allowed to rise to a peak of 4 amps, enabling injectors to open quickly, and is then reduced to one amp, holding them open. This is called "peak and hold". If current can't reach a 4-amp peak, Code 65 is set. This code is also set if an injector driver circuit is shorted to voltage.

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

1. The following conditions must be present to set a Code 65: The 4-amp injector current was not reached on each circuit. Battery voltage greater than 9 volts. Injectors pulsed "ON" longer than calibrated pulse width. The above conditions met for 20 seconds.
2. Checks ECM and harness wiring to 3-terminal injector harness connector.
3. This test checks for open injector harness or injector. NOTE: Although shorted harness or injector will not set a Code 65, problem should be corrected if discovered.
4. Results of step 2) will determine which branch to follow on Code 65 flow chart (2 of 2).
5. Each harness was confirmed as being okay in steps 2) and 3). This test will check remainder of circuit from injectors to ECM.
6. Identifies cause of high resistance found in step 3). A short or low resistance will not cause Code 65, but should be corrected.
7. This test checks for grounded "peak and hold" jumpers. This condition would allow injectors to pulse, but would not allow "peak and hold" operation as current would not flow through resistor in ECM.

An open in circuits No. 467, 468, 966 or 967, or circuits No. 467 or 468 shorted to voltage will cause a Code 65 to be set and will also cause misfire due to an inoperative pair of injectors. Circuits No. 966 and 967 shorted to ground will cause a Code 65 to be set, while allowing injectors to pulse. An intermittent problem would have to be present for at least 20 seconds to set Code 65.

Code 65 Schematic, Fuel Injector Current Low. Scheme 340

Code 65 Flow Chart (1 of 2), Fuel Injector Current Low. Scheme 341

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

1. 8) This checks for short to voltage in injector driver circuits. It is necessary to crank engine to assure voltage to circuit No. 120.
2. 9) Determines if injector driver circuits No. 467 and 468 are shorted to ground.
3. 10) This checks the output at the ECM to determine if circuits No. 467 and 468 are okay.
4. 11) Checks for proper continuity of "peak and hold" jumpers circuits No. 966 and 967.

Code 65 Flow Chart (2 of 2), Fuel Injector Current Low. Scheme 342

CODE 66, A/C PRESSURE SENSOR VOLT OUT OF SPECS

The A/C pressure sensor responds to changes in A/C refrigerant system high side pressure. ECM uses this information to determine how much load is being placed on the engine during A/C compressor operation. This information is used to determine IAC valve position for idle speed control. A 5-volt reference signal and ground are both provided by ECM. A signal line is also provided to the ECM. The signal received by ECM is proportional to A/C system pressure. Operational range of the sensor is 0-450 psi (or about .1-4.9 volts). If voltage falls outside calibrated range for 5 seconds or more, a Code 66 will be set. A/C compressor is disabled by the ECM when a Code 66 is set.

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

1. This test checks voltage signal being received by ECM from A/C pressure sensor.
2. This test checks to see if high voltage signal is caused by shorted sensor or short to voltage in circuit. Normally, unplugging sensor would cause a normal circuit to reduce to near zero volts.
3. Determines if low voltage is from sensor or circuit. This is accomplished by jumpering sensor signal circuit No. 380 to 5 volts. This will check circuit, connections and ECM.
4. Since the prior step eliminated pressure switch, this test checks to see if low voltage signal was caused by an open in sensor circuit or 5-volt reference circuit.

Code 66 sets when signal voltage falls outside the normal possible range of the sensor and is not due to a refrigerant system problem. If problem is intermittent, check for opens or shorts in harness, or poor connections. If okay, replace A/C pressure sensor. If Code 66 resets again, replace ECM.

Note. Code 66 will set on non-A/C vehicles if circuit No. 450 to terminal "BC3" is open or shorted to battery voltage.

Code 66 Schematic, A/C Pressure Sensor Volt Out Of Specs. Scheme 343

Code 66 Flow Chart, A/C Pressure Sensor Volt Out Of Specs. Scheme 344

CHART C-1A, PARK/NEUTRAL SWITCH (A/T ONLY)

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

1. This test checks for a closed switch to ground in Park position.
2. This test checks for an open switch in Drive range.
3. Ensure that "Scan" tester indicates Drive while wiggling shifter to test for a faulty or misadjusted switch.

Chart C-1A Schematic, Park/Neutral Switch (A/T Only). Scheme 345

Chart C-1A, Park/Neutral Switch (A/T Only). Scheme 346

CHART C-1D, MAP OUTPUT CHECK

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

1. Checks MAP sensor output voltage to ECM. This voltage, without engine running, represents a barometer reading to ECM.
2. Applying vacuum to MAP sensor should cause voltage to be 1.2-2.3 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 leaks or restriction. Ensure no other vacuum devices are connected to MAP sensor signal hose.

Chart C-1D, MAP Output Check. Scheme 347

CHART C-1E, POWER STEERING PRESSURE SWITCH

Power steering pressure switch is normally open to ground and circuit No. 495 will be near battery voltage. Turning the steering wheel increases power steering oil pressure and its load on an idling engine. The pressure switch will close before the load can cause an idle problem. Closing the switch causes circuit No. 495 to read less than one volt. The ECM will increase the idle air rate and de-energize A/C relay. Pressure switch that will not close, or an open circuit No. 450 or 495 may cause the engine to stop when power steering loads are high. A switch that will not open, or a short to ground on circuit No. 495, may affect idle quality and will cause A/C relay to de-energize.

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

1. Different brands of "Scan" testers may display the state of this switch in different ways. Refer to "Scan" tester operator's manual to determine how input should be read.
2. Checks to determine if circuit No. 495 is shorted to ground.
3. This should simulate a closed switch.

Chart C-1E Schematic, P/S Pressure Switch. Scheme 348

Chart C-1E, P/S Pressure Switch. Scheme 349

CHART C-2A, INJECTOR BALANCE TEST

Note. If it is determined that injectors are dirty, they should be cleaned using approved injector cleaning procedures prior to performing this test. Complete CHART A-7, FUEL SYSTEM DIAGNOSIS before starting this test.

The injector balance test is used to pulse the injector for a precise amount of time, spraying a measured amount of fuel in the intake manifold. As each injector is pulsed, a drop in fuel rail pressure occurs. This pressure drop can be recorded and compared to other injectors. An injector that has a pressure drop of 1.5 psi (.11 kg/cm 2 ) or more, greater than or less than other injectors, should be considered faulty.

Note. Allow engine to cool down to avoid irregular readings due to "Hot Soak" fuel boiling. In order to prevent flooding, the INJECTOR BALANCE TEST should not be repeated more than once, without starting and running engine.

1. With ignition off, connect Fuel Pressure Gauge (J 34730-1 ) to pressure tap. Unplug harness connector at all injectors. Connect Injector Tester (J 34730-3 ) to one of the injectors.
2. Follow manufacturer's instructions for use of the adapter harness. Ignition should be turned off at least 10 seconds to complete ECM shutdown cycle.
3. Turn ignition on. Fuel pump should run at least 2 seconds after ignition is turned on. Bleed air from gauge and hose to ensure accurate gauge reading. Repeat this procedure until all air is bled from system. Turn ignition off for at least 10 seconds.
4. Turn ignition on again to bring fuel pressure to maximum. Record initial pressure reading. Energize tester one time and note pressure drop at lowest point.
5. Disregard any slight pressure drop after low point is reached. Subtracting second pressure reading from initial reading indicates amount of injector pressure drop.
6. Repeat test step 4) on each injector and compare amount of pressure drop. Recheck injectors that do not read within pressure drop range. Replace injector(s) that fail second check.
7. If injectors are all okay, plug in harness connectors and review SYMPTOMS in TROUBLE SHOOTING section.

CHART C-2C, IDLE AIR CONTROL (IAC) VALVE CHECK

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, display will indicate 5 counts or less. Intermittently, an erratic or unstable idle may occur. Engine speed may vary 200 RPM or more, greater than or less than specified RPM. Unplug IAC and check to see if the condition changes. If condition does not change, IAC is not at fault.
2. Once engine is turned off, IAC valve is retracted to a fixed (park) position for increased airflow and idle speed, prior to next engine start. A "Scan" tester will display 100 or more counts.
3. The IAC valve should extend, as ECM commands idle speed to decrease to the desired RPM.
4. Ensure that IAC valve is unplugged prior to this test. Test light will confirm ECM signals by a steady or flashing light on all circuits.
5. It is remotely possible that one of the circuits is shorted to voltage, which would have been indicated by a steady light. Unplug ECM. Turn ignition on and probe terminals to check for shorts.

Low unstable idle may be caused by a system problem that cannot be corrected by the IAC. "Scan" counts will be more than 60, if idle is too low. If idle is too high, counts will be 5 or less. If idle speed is excessively high, locate and correct vacuum leak. Check for the following conditions

1. System is too lean (high air/fuel ratio) and idle speed is either too high or too low. Engine speed vary from high to low, and unplugging IAC does not help. A Code 44 may be set. A "Scan" tester and/or voltmeter will indicate an O2 sensor output less than 300 mV (.3 volt). Check for low fuel pressure or water in fuel. A lean exhaust, with O2 sensor output fixed greater than 800 mV (.8 volt), indicates a contaminated sensor. This contamination is usually caused by silicone and may also set a Code 45.
2. System is too rich (low air/fuel ratio) and idle speed may be too low. The "Scan" tester will usually indicate counts greater than 80. Since fuel system is rich, Black exhaust smoke may be exhibited. A "Scan" tester and/or voltmeter will indicate a O2 sensor signal fixed greater than 800 mV (.8 volt). Check for high fuel pressure. Also check for injector leaking or sticking.
3. Check throttle body by removing IAC and inspecting bore for foreign material. Check for evidence of IAC valve seat or pintle being damaged.
4. Refer to ROUGH, UNSTABLE OR INCORRECT IDLE symptom «CCC EFI TESTS W/O CODES»(/buick/skylark/vi-1986-1992/remont/testing-diagnostics/#ccc-efi-tests-wo-codes) .

Chart C-2C Schematic, IAC Valve Check. Scheme 350

Chart C-2C, IAC Valve Check. Scheme 351

CHART C-3, CANISTER PURGE VALVE CHECK

If diagnostic test terminal is grounded with engine stopped or the following conditions are met with engine running, purge solenoid is energized (purge on).

1. Engine has been operating for more than 65 seconds.
2. Coolant temperature greater than 133°F (56°C).

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

1. Checks to see if solenoid is opened or closed. The solenoid is normally de-energized in this test and should be open.
2. This test checks for a complete circuit. Normally ignition voltage is present at circuit No. 439. ECM provides ground on circuit No. 428.
3. Functional test is completed by grounding test terminal. Normally this should energize solenoid, opening valve and allowing vacuum to drop (purge on).

Chart C-3 Schematic, Canister Purge Valve Check. Scheme 352

Chart C-3, Canister Purge Valve Check. Scheme 353

CHART C-4M, INTEGRATED DIRECT IGNITION (IDI) MISFIRED DIAGNOSIS

The IDI system uses a waste spark method of distribution. This type of ignition system allows the module to trigger both the No. 1 and No. 4 coil pair, resulting in both No. 1 and No. 4 spark plugs firing simultaneously. No. 1 cylinder is on compression stroke the same time No. 4 is on exhaust stroke, resulting in a lower energy requirement to fire No. 4 spark plug. This allows the remainder of high voltage to be used to fire No. 1 spark plug. On this application, crank sensor is mounted to/and protrudes through the engine block to within about .050" (1.3 mm) of crankshaft reluctor. Since the reluctor is a machined portion of crankshaft, and sensor is mounted in a fixed position on engine block, timing adjustments are not possible or necessary.

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

1. This test checks for equal relative power output between the cylinders. Any injector, when unplugged, that does not cause a drop in engine RPM, is responsible for misfire condition.
2. If plug boot is burned, the other plug on that coil may still fire at idle. This step tests system's ability to produce at least 25,000 volts at each spark plug.
3. A coil that has no spark to either spark plug, may have an open secondary circuit. If this condition exists, coil's secondary resistance should be checked. Resistance readings greater than 20,000 ohms, but not infinite, probably will not cause a no-start condition. However, this may cause an engine miss under certain conditions.
4. Test light will blink if no-spark condition is caused by faulty coil connections, coil or secondary boot assembly. If light does not blink, fault is in module connections or module.
5. This step checks for an open injector driver circuit and for ignition voltage feed to the injector.
6. An injector driver circuit shorted to ground would result in test light illumination, and possibly a flooded condition which could damage engine. A shorted injector (less than 2 ohms) could cause incorrect ECM operation.

Verify IDI connector terminal "K" (circuit No. 450) resistance to ground is less than .5 ohm. A shorted or low resistance injector may cause a miss in the other injector in that pair.

Chart C-4M Schematic, IDI Misfire Diagnosis. Scheme 354

Chart C-4M, IDI Misfire Diagnosis. Scheme 355

CHART C-5, ESC SYSTEM CHECK

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

1. With engine idling, a knock signal should not be present at ECM, as detonation is not likely under no-load condition.
2. Tapping on the engine lift hook bracket should simulate a knock condition. This will determine if knock sensor is capable of detecting detonation. If knock is not detected, try tapping on engine block near sensor. If knock is still not detected, replace sensor.
3. If engine has an internal problem that is simulating a knock, the knock sensor may be responding to that condition. Internal problem should be diagnosed and repaired.
4. This test determines if the knock sensor is faulty, or the ESC portion of the MEM-CAL is faulty. If MEM-CAL is at fault, ensure that it is properly installed and latched in place. If not properly installed, repair and retest.

While observing "Scan" tester, a knock should be indicated whenever detonation is present (heard). Detonation is most likely to take place under high engine load condition.

Chart C-5, ESC System Check. Scheme 356

CHART C-8A, TCC ELECTRICAL DIAGNOSIS

The TCC will engage under the following conditions

1. Vehicle road speed exceeds calibrated value of about 34 MPH (55km/h).
2. TPS not varying signal, indicating a steady road speed.
3. Transmission 2nd gear switch closed.
4. Brake switch closed.

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

1. If light is not illuminated, this confirms transmission 2nd gear apply switch is open.
2. Transmission 2nd gear apply switch should close at 25 MPH. Test light should illuminate and confirm battery voltage, and closed brake switch.
3. Grounding diagnostic terminal with ignition on and engine off, should energize TCC solenoid. When terminal is grounded, circuit No. 422 is simultaneously grounded. This test ECM's ability to supply a ground to the TCC solenoid. Test light should illuminate when connected to battery voltage and ALDL terminal "F". This illumination occurs as circuit No. 422 is grounded.

"Scan" tester will only indicate whether ECM has turned on TCC driver, and does not confirm that TCC has engaged. Check for RPM drop as "Scan" tester indicates TCC driver has been turned on. If RPM drops occurs, TCC has engaged.

Chart C-8A Schematic, TCC Electrical Diagnosis. Scheme 357

Chart C-8A, TCC Electrical Diagnosis. Scheme 358

CHART C-8C, MANUAL TRANSMISSION SHIFT LIGHT

The shift light indicates the best transmission shift point for maximum fuel economy. The light is controlled by the ECM and is turned on by grounding circuit No. 456. The ECM uses information from the following inputs to control the shift light

1. Coolant temperature must be greater than 14°F (-10°C).
2. By comparing vehicle speed (from VSS) to engine RPM, ECM can determine that transaxle has been in gear for least 1.2 seconds.
3. TPS calibration is between minimum and maximum values for each gear.
4. RPM has exceeded calibrated value of 6500 RPM maximum, for each gear.

The shift light will be illuminated after a calibrated delay time, which is dependent on last gear change or downshift. Light will remain on for a minimum of 10 seconds.

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

1. This should not turn on shift light. If the light is on, a short to ground in circuit No. 456 wiring exists, or ECM is faulty.
2. When the diagnostic terminal is grounded, ECM should ground circuit No. 456 and shift light should illuminate.
3. This checks the shift light circuit up to ECM connector. If shift light illuminates, ECM connector is faulty or ECM has lost the ability to ground circuit No. 456.

Ground ALDL and check for Code 24 (VSS). Also check for faulty thermostat or incorrect heat range. Check for incorrect or faulty PROM.

Chart C-8C Schematic, M/T Shift Light. Scheme 359

Chart C-8C, M/T Shift Light. Scheme 360

CHART C-8D, TRANSMISSION GEAR SWITCHES CIRCUIT CHECK

This chart will check 2nd and 3rd gear switch inputs to ECM. Transmission gear input signals to ECM are determinate as follow

GEAR INPUT SIGNALS

Note. Test numbers refer to test numbers on diagnostic chart

1. This check for an open or grounded circuit between transmission connector and ECM. since ECM terminals are normally high, battery voltage should be indicated at both terminals with connector removed. A DVOM must be used for this first step.
2. A test light to battery is used in this step to check transmission switch or normal state. This is 1st gear (or Park/Neutral) state. The test light must be "ON" for normal closed (N.C.) 2nd gear switch . Used of Wiring Probe Kit (J-35616) will assist here and step 3).
3. This checks if transmission switch function normally. In 3rd gear both switch should have changed from there original 1st gear state.

Sticky or improperly functional 2nd or 3rd gear switch may cause Code 26 to set intermittently.

Chart C-8D Schematic, Trans Gear Switches. Scheme 361

Chart C-8D, Trans Gear Switches Circuit. Scheme 362

CHART C-10, A/C CLUTCH CONTROL CIRCUIT DIAGNOSIS

When A/C compressor is activated, ECM provides a ground path through circuit No. 459, energizing A/C clutch control relay. A/C clutch is delayed about .3 second after A/C is requested. This time lapse allows IAC to adjust RPM for the additional engine load. The ECM will temporarily disengage A/C clutch relay for calibrated times for one or more of the following conditions

1. Hot engine restart.
2. Wide Open Throttle (WOT), TPS greater than 90 percent.
3. Power steering pressure high or pressure switch open.
4. Engine speed greater than about 6000 RPM.
5. During IAC motor reset.

If Code 66 is present, A/C clutch relay will remain disengaged. A/C clutch relay will remain disengaged if there is no request for A/C or low pressure switch.

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

1. Engine must be running for ECM to energize A/C relay. This test will determine is relay or circuit No. 459 is at fault.
2. This test determines if signal is reaching ECM through circuit No. 66 from A/C control panel. Signal should only be present when A/C mode or defrost mode has been selected.
3. If ECM is receives high power steering pressure signal, the A/C clutch will be disengaged by ECM.
4. With engine idling and A/C on, ECM should ground circuit No. 459. This should result in test light being illuminated.

If original problem was insufficient cooling from A/C system, problem may be caused by inoperative cooling fan. See CHART C-12, for cooling fan diagnosis. "Scan" tester pressure should be within 20 psi of actual. If not within 20 psi of actual, check for circuit problem using Code 66 chart or replace sensor.

Chart C-10, A/C Clutch Control Circuit. Scheme 363

CHART C-12, COOLING FAN FUNCTIONAL CHECK

The electric cooling fan is controlled by ECM through fan relay, based on inputs from the coolant and manifold air temperature sensors, A/C control switch, A/C pressure sensor and vehicle speed sensor. ECM controls cooling fan by grounding circuit No. 536 which activates fan relay.

Fan relay is commanded on under the following conditions

1. "Scan" tester indicates coolant temperature 103-106°C or greater.
2. A/C clutch request.
3. Vehicle speed less than 35 MPH.

Fan relay is commanded on regardless of vehicle speed under the following conditions

1. A Code 14 or 15 is set.
2. "Scan" tester indicates coolant temperature 115-118°C or greater.
3. A/C pressure is high.

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

1. With diagnostic terminal grounded, cooling fan control drivers will close. This should energize the fan control relay.
2. This test checks to see if fault is in wiring to fan, or fan connection.

If overheating condition exists, it should be determined if condition is diagnosed because of an actual boilover, warning light illumination or temperature gauge indication. If gauge or light indicates overheating, but boilover is not present, gauge or light circuit should be checked. The accuracy of the gauge (or light) can be checked by comparing the coolant temperature sensor reading with gauge reading. This can be accomplished by using a "Scan" tester. If it has been determined that engine is actually overheating, but cooling fans are not switching on, this indicates coolant temperature sensor has shifted out of calibration and should be replaced. If vehicle is overheating and cooling fans are operating properly, cooling system should be checked.

Chart C-12, Cooling Fan Functional Check. Scheme 364

Scheme 365

Scheme 366

PIN VOLTAGE CHARTS

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

The following conditions must be met before testing

1. Engine at operating temperature.
2. Engine in "closed loop" operation.
3. Engine idling ("Engine Run" column).
4. ALDL "test" terminal NOT grounded.
5. Scanner or ALDL tool NOT installed.

Scheme 367

Scheme 368

2.3L Engine PFI CCC Wiring Diagram. Scheme 369

See also:
• CCC EFI TESTS W/O CODES
• PIN VOLTAGE CHARTS
• INPUT SIGNALS