For 1990-2009 cars

# CHASSIS MANUAL VOLUME II REVISIONS

#### VEHICLES AFFECTED: 1987 DELTA 88 AND NINETY-EIGHT

The diagnostic charts on pages 33-3, 33-4 and 33-5 of the C/H Car Section have been revised.

Please update your 1987 Firenza-calais-Cutlass Ciera-Delta 88-Ninety-Eight Chassis Service Manual Volume II with these revised pages.

VEHICLE SPEED SENSOR: PERMANENT MAGNET GENERATOR

(Continued from previous page)

B: VEHICLE SPEED SENSOR BUFFER OUTPUT TEST (TABLE 1)

Measure: VOLTAGE

At: VEHICLE SPEED SENSOR BUFFER CONNECTOR C 1 (Disconnected)

#### Conditions:

Ignition Switch: RUN Cruise Switch: ON

Measure Correct Between Voltage For Diagnosis ------- ------- -------------- F (DK GRN) 5 Volts or See 1 & Ground greater

C (BRN/WHT) Battery See 2 & Ground

- Trip Calculator, and Chime Module connectors: DISCONNECTED.

- Cruise Control: CONNECTED

D (RED) & 5 Volts or See 3 Ground greater

- Trip Calculator: CONNECTED - Cruise Control Module and Chime Module Connectors: DISCONNECTED

D(RED) & 5 Volts or See 4 Ground greater

- If voltages are correct, go to Table 2.

1. Check DK GRN (389) wire for an open. Check that connector C200 is properly mated. See Section 80, 81, or 82 for further diagnosis.

2. Check BRN/WHT and BRN (437) wire for an open. Check that connector C260 is properly mated. If OK, replace ECM.

3. Check RED (381) wire for an open ( see schematic). If OK, replace Cruise Control Module.

4. Check RED (381) wire for an open (see schematic). If OK, replace Trip (Auto) Calculator.

B: VEHICLE SPEED SENSOR BUFFER OUTPUT TEST (TABLE 2)

Measure: VOLTAGE

At: VEHICLE SPEED SENSOR BUFFER CONNECTOR C 1 (Connected)

#### Conditions:

- Cruise Switch: ON - Ignition Switch: RUN - Gear Selector: NEUTRAL - Turn drive wheels by hand while making measurements

Measure Correct For Diagnosis Between Voltage ------------- ------- ------- Varying from F (DK GRN) less than 1 See 1 & Ground volt to more than 4 volts

Varying from D (RED) & less than I See 1 Ground volt to more than 2.5 volts

Varying om C (BRN/WHT) less than l See l & Ground volt to more than 4 voits

- If voltages are correct, replace the inoperative component.

- If voltages are correct and Trip (Auto) Calculator is inoperative, replace it.

- If voltages are correct and Cruise Control Module is inoperative, replace it.

- If voltages are correct and Speedometer or Odometer is inoperative, go to Test C2. (Indicators and Gages Clusters) Digital Clusters should be sent to an approved A/C Delco repair Station.

1. Replace Vehicle Speed Sensor Buffer.

C: SPEEDOMETER IS INACCURATE

1. Plug in Scan tool to ALDL Connector at lower left of I/P near steering column. With Scan tool on and set to proper mode (RPM/ Speed), operate vehicle at constant speeds. Observe the speedometer and Scan tool dis- play.

- If they are in agreement +/- 2 mph. the Speedometer is good. Check for correct tire size and inflation, and axle ratio gear calibration (see Section 7A). If all are correct, replace the VSS Buffer.

- If Scan tool and speedometer are not in agreement +/- 2 mph, go to Step 2 (Indicator and Gages Cluster). With Digital Clusters, send Cluster to an approved A/C Repair Cen- ter for repair.

2. (Indicators and Gages Cluster). Remove I/P Cluster. See Section 8C for Cluster Removal. Connect I/P tester J-33431 to circuit board on underside of I/P Cluster using 3 terminal edge board connector J-33431-9. With the tester plugged in and set to ON, 54 mph. and 60 Hz, the Speedometer should read 54 mph +/- 2 mph.

If the Speedometer does not indicate properly, the Speedometer is to be sent to an approved A/C Repair Center for repair.

If the Speedometer operates properly, replace the VSS Buffer.

D: ODOMETER(S) DO NOT OPERATE CORRECTLY

1. Remove the I/P Cluster. See Section 8C for Cluster Removal. Disassemble the cluster and remove the small Odometer connectors from the Speedometer circuit board. Connect I/P tester J-33431-3. Plug in the I/P tester and set it to ON, 54 mph, and 60 Hz. With the Odometer test switch held down, the Odometer should turn and change the mileage shown, about 1.8 mile per minute.

- If the Odometer does not turn, replace the stepper motor (see Section 8C).

- If the Odometer turns about 2.9 miles per minute, a metric Odometer could have been installed. Check to see that the correct Odometer assembly was installed (see SecTion 8C).

E: MODULE SHORT TEST

1. Disconnect Chime Module, Trip Calculator and Cruise Control Module Connectors, operate vehicle and observe the Speedometer.

- If the Speedometer works, go to Step 2.

- If the Speedometer does not operate, check the RED (381) wire for a short to ground. If OK go to Test A.

2. Reconnect the Chime module, Trip Calculation and Cruise Control one at a time. Operate vehicle after reconnecting each of the above and observe the Speedometer.

- If the Speedometer does not work replace the module which caused the speedometer not to operate.

- If Speedometer works, check RED (381) wire for an intermittent short to ground.

#### CIRCUIT OPERATION

The Vehicle Speed Sensor (VSS) generates a signal that indicates the speed of the vehicle. This signal is processed by the Solid State Vehicle Speed Sensor Buffer to supply inputs to the Electronic Control Module (ECM), the Speed- ometer, the Cruise Control Module (if equipped), and the Trip (Auto) Calculator (if equipped).

The Vehicle Speed Sensor is mounted in the Transaxle. A magnet rotates near a coil, producing vol tage pulses in the coil. The frequency coming from this coil depends on the vehicle speed. As the speed increases, so does the number of voltage pulses per second.

The Vehicle Speed Sensor Buffer takes the voltage pulses from the Sensor and uses them to close three Solid State output switches. Each output terminal is switched to ground at a rate that is proportional to the speed of the car. The Sensor generates 40,000 pulses per mile (ppm). The Speedometer is switched at a frequency of 4,000 ppm. The ECM and the Cruise Control use a lower frequency, 2,000 ppm.

The output switches in the Vehicle Speed Sensor Buffer are Solid State switches, not mechanical ones. Self-powered test lamps or ohmmeters should not be used to test them. Do not measure the resistance at the output of the buffer.

SYMPTOM TABLE

SYMPTOM FOR DIAGNOSIS

Speedometer does not operate Do Test A properly and ECM Code 24 is set

ECM Code 24 is set See Section 6E for Speedometer diagnosis operates properly

Speedometer does Do Test B not operate properly, ECM Code 24 is not set

Cruise Control does Do Test B not operate properly, ECM Code 24 is not set

Speedometer and/or Do Test C Odometer(s) are inaccurate

Odometer(s) are DoTest D inoperative or inaccurate

Speedometer, Do Test E Odometer, Cruise Control, and Turn Signal On Reminder do not operate

A: VEHICLE SPEED SENSOR BUFFER TEST (TABLE 1)

Measure: VOLTAGE

At: VEHICLE SPEED SENSOR BUFFER CONNECTOR C 1 (Disconnected)

#### Condition:

- Ignition Switch: RUN

Measure Correct For Diagnosis Between Voltage

A (PNK/BLK) Battery See 1 &Ground

A(PNK/BLK &B (BLK/WHT Battery See 2

- If voltages are correct, go to Table 2.

1. Check PNK/BLK (239) wire for an open (see schematic).

2. Check BLK/WHT (450) wire for an open (see schematic). Check that

A: VEHICLE SPEED SENSOR BUFFER TEST (TABLE 2)

Measure: VOLTAGE

At: VEHICLE SPEED SENSOR BUFFER CONNECTOR C2 (Disconnected)

#### Conditions:

- Ignition Switch: RUN - Gear Selector: NEUTRAL - Turn drive wheels by hand while making measurernents

Measure Correct AC Between Voltage For Diagnosis ------- ------- ------------- C (YEL) & A Between 1 and See l (PPL) 5 volts AC

- If voltages are correct, replace Vehicle Speed Sensor Buffer.

1. Check YEL (400) and PPL (401) wires (see schematic). If both wires are OK, replace Vehicle Speed Sensor.

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.