CHASSIS MANUAL REVISIONS AFFECTED PAGES LISTED

Models/Years: 1986 TORONADO

The following pages and charts have been updated in the 1986 Toronado Chassis Service Manual. The revisions are noted in the shaded areas.

1. Pages 6E3-A-16 and 6E3-A-17 of the Drive ability and Emissions Section. 2. The "EGR System Fault" information on page 8Dl-28 and diagnostic chart on page 8D1-29 3. Step 1 under Test Description on page 8D1-30 4. Mass Air Flow Sensor Code E033 Diagnostic Chart on page 8D1-31 5. Step 1 and 2 under Test Description on page 8D1-32 6. Mass Air Flow Sensor Code E034 Diagnostic Chart on page 8D1-33 7. The CAM Sensor Circuit Failure Diagnostic Chart on page 8D1-41 8. The C31 EST or Bypass Circuit Failure Diagnostic Chart on page 8D1-43

Please update your 1986 Toronado Chassis Service Manual with these revised pages.

CHART A-3 ENGINE CRANKS BUT WON'T RUN (Page 2 of 3)

Circuit Description: For timing of spark plug firing, a cam sensor "hall effect" switch is used. The cam sensor sends a signal (Sync-Pulse) to the ignition module when cylinder #1 is 25 deg after top dead center on the compression stroke. This signal is used to start the correct sequence of coil firing and to enable sequential fuel injection. The engine will continue to run if the cam signal is lost while running, however, will not restart after shut down and a Code E041 will be stored.

The crank sensor sends a signal to the ignition module and then to the ECM for reference rpm and crankshaft position. There are three windows in a disc (interruptor) which is mounted to the harmonic balancer. These windows pass by the sensor and as each window passes, the next coil is triggered.

Test Description: The following numbered steps correspond with the step numbers on the diagnostic chart.

8. Verifies ignition feed voltage at terminal "M" of the C3I module. Less than battery voltage would be an indication of a CKT 639 fault.

9. The test light to 12 volts simulates a reference signal to the ECM which will result in an injector test light blink if the CKT 430, the ECM and the injector driver circuit are all OK.

10. If the Cam Sensor signal circuit terminal "A" is jumpered to the ground circuit terminal "B", the response will be an injector test light blink. This is a result of this artificial "Cam Signal" being transmitted through the C31 module to ECM terminal "All" and the ECM activating the injection driver circuit.

11. Verifies a proper Cam signal circuit voltage of 7 to 9 volts and a good ground from the C3I module to terminal "B" of the sensor connector.

12. Determines if reason for incorrect voltage reading was due to a fault in CKT 633, an open in CKT 632 or a faulty C31 module.

CODE E032 EGR SYSTEM FAULT

Circuit Description:

The EGR Vacuum Control is operated by an Electronic Vacuum Regulator Valve (EVRV). The EVRV is comprised of an EGR Vacuum Control Solenoid and a EGR Diagnostic Vacuum Switch.

The EGR Solenoid is Pulse Width Modulated by the ECM and controls the vacuum to the EGR valve. The Solenoid is vented and is equipped with a filter.

The normally open EGR Diagnostic Vacuum Switch monitors the vacuum to the EGR Valve and signals the ECM when control vacuum is applied to the valve (switch closes). The ECM will not energize the solenoid in "Park", "Neutral", or at idle.

The ECM cycles the EGR valve "ON" and "OFF" (Pulse Width Modulation). For this reason, the EGR valve is never continuously open but always "pulsed" which may be monitored by observing the ECM input E160 (EVRV Switch) during normal EGR operation. "HI" indicates the EGR is off and "LO" indicates it is on.

Code E0042032 will set if the vacuum switch closes at idle, or if it does not close under load (less than WOT).

o Engine running. o Code E033 or E034 not present o Coolant temperature above 42.5 deg C (108 deg F). o LV8 reading less than 144 cts. o Conditions exist over 9.6 seconds

Test Description: The following numbered steps correspond with the step numbers on diagnostic charts.

1. EI60 displays the condition diagnostic switch. In park or neutral, the display should read "HI" (open switch).

2. Under moderate engine load the display will switch from "HI" to "LO".

3.* Checks the integrity of the 12V feed and ground circuits. If these circuits check OK, the fault is elsewhere in the EVRV/EGR Control circuit.

4.* A test light connected "A" to "B" will verify the integrity of the ECM wiring and check for proper ECM operation.

5. If "LO" was displayed at idle disconnect the EVRV harness. If display remains "LO", the fault is either a short to ground in CKT 435 or the ECM.

6. If the EI60 display switches from "LO" to "HI" when the EVRV is disconnected, the fault is either a in the EVRV/EGR Solenoid, CKT 357 or the ECM. Probing at terminal "B" will further isolate the fault. If the test light is on, disconnect ECM A-B connector before checking CKT435 for a short to ground since the short could be inside the ECM.

Diagnostic Aids: An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside the insulation.

Check For:

o POOR CONNECTION OR DAMAGED HARNESS: Inspect ECM harness connectors for backed out terminal "D9", improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection and damaged harness.

o INTERMITTENT TEST: If connections and harness checks out ok, monitor EI60 (EVRV Switch) display while moving related connectors and wiring harness. If the failure is induced, the "EVRV Switch" display will abruptly change. This will help to isolate the location of the malfunction.

CODE E033 MASS AIR FLOW (MAF) SENSOR FREQUENCY HIGH

Circuit Description:

The Mass Air Flow (MAF) sensor measures the amount of air which passes through it in a given time. The ECM uses this information to monitor the operating condition of the engine, in calculating fuel delivery. A large quantity of air movement indicates acceleration, while a small quantity indicates deceleration or idle.

The MAF sensor produces a frequency signal which cannot be easily measured. The sensor can be diagnosed using the procedures on this chart and with the aid of MAF sensor tester J-36101 or equivalent.

Code E033 will set when the following conditions are met: o E021 or E022 not present o Engine is running at less than 800 RPM o TPS is less than 500mv o Air Flow more than 150 grams per second o All of the above are met for 5 seconds or more

Test Description: The following numbered steps correspond with the step numbers on the diagnostic chart.

1. The Diagnostic Display, ED21 (MAF), is of little use in diagnosing this fault, because when the code is set, a default based on TPS is displayed in place of the actual MAF input to the ECM. If the Mass Air Flow Sensor fault is still present, Code E033 should reset within one minute. If the code does not reset, the fault was intermittent and MAF Sensor tester J-36101 or equivalent should be used to test the sensor.

2. Inspect wire routings of high voltage wires, such as spark plug wires. Such wires routed too closely to MAF wiring harness could possibly cause an intermittent Code E033.

Diagnostic Aids:

An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside the insulation.

Check For:

o POOR CONNECTION OR DAMAGED HARNESS INSPECT: ECM harness connectors for backed out terminal "B6", improper mating, broken locks, improperly formed or damaged terminals,poor terminal to wire connection and damaged harness.

o INTERMITTENT TEST: If connections and harness checks out ok, monitor ED21 (MAF) display while moving related connectors and wiring harness. If the failure is induced, the "MAF" display will abruptly change. This will help to isolate the location of the malfunction.

o MISS-ROUTED HARNESS: Inspect MAF sensor harness to insure that it is not too close to high voltage wires, such as spark plug leads.

o MISCALIBRATED MAF SENSOR: The Mass Air Flow Sensor may be tested for being out of specification by using a MAF Sensor test tool J-36101 or equivalent

CODE E034 MASS AIR FLOW (MAF) SENSOR FREQUENCY LOW

Circuit Description:

The Mass Air Flow (MAF) sensor measures the amount of air which passes through it in a given time. The ECM uses this information to monitor the operating condition of the engine, in calculating fuel delivery. A large quantity of air movement indicates acceleration, while a small quantity indicates deceleration or idle. The MAF sensor produces a frequency signal which cannot be easily measured. The sensor can be diagnosed using the procedures on this chart and with the aid of MAF sensor tester J-36101 or equivalent.

Code E034 will set when either of the following sets of conditions exists: o Engine running o No MAF sensor signal for 250 m sec. OR o Engine running over 1400 rpm o TPS over 2.5 volts o Air Flow less than 10 grams per second (low frequency) o Above conditions for over 10 sec.

Test Description: The following numbered steps correspond with the step numbers on the diagnostic chart.

1. The Diagnostic Display, ED21 (MAF), is of little use in diagnosing this fault, because when the code is set, a default based on TPS is displayed in place of the actual MAF input to the ECM. A loose or damaged air duct may set a Code E034 and must be checked. If the Mass Air Flow Sensor fault is still present, Code E034 should be reset within one minute. If the code does not reset, the fault was intermittent, and MAF Sensor tester J-36101 or equivalent should be used to test the sensor.

2. This step verifies that the reference signal from the ECM is present at MAF sensor harness connector terminal "B". Less than 4 or over 6 volts at this point indicates a faulty CKT 492, connection, or ECM.

3. Verifies that both ignition voltage and a good ground circuit are available.

Diagnostic Aids:

An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside the insulation.

Check For:

o POOR CONNECTION OR DAMAGED HARNESS: Inspect ECM harness connectors for backed out terminal "B6", improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection and damaged harness.

o INTERMITTENT TEST: If connections and harness checks out ok, monitor ED21 (MAF) display while moving related connectors and wiring harness. If the failure is induced, the "MAF" display will abruptly change. This will help to isolate the location of the malfunction.

o MISS-ROUTED HARNESS: Inspect MAF sensor harness to insure that it is not too close to high voltage wires, such as spark plug leads.

o MISCALIBRATED MAF SENSOR: The Mass Air Flow Sensor may be tested for being out of specification by using a MAF Sensor test tool J-36101 or equivalent

DIAGNOSTIC AIDS: An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside the insulation.

Check For:

o POOR CONNECTION OR DAMAGED HARNESS: Inspect ECM harness connectors for backed out terminal "A11", improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection and damaged harness.

o INTERMITTENT TEST: If connections and harness checks out ok, monitor A Digital Voltmeter connected from ECM terminal "A11" to ground while moving related connectors and wiring harness. If the failure is induced, the voltage reading will abruptly change. This will help to isolate the location of the malfunction.

o SYMPTOM INDICATORS:

- If Cam Signal from Cam Sensor to C31 module is lost while running, engine will not restart after shutdown.

- If Cam Signal output from the module or wiring etc., to the ECM has failed, engine will restart after shutdown.

General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.