• Troubleshooting Tips
If the amplitude is low, look for an excessive air gap between the trigger wheel and the pickup.
If the amplitude wavers, look for a bent axle.
If one of the oscillations looks distorted, look for a bent or damaged tooth on the trigger wheel.
O
2
S Normal - Zirconia
• Theory of Operation
An O
2
sensor provides an output voltage that represents the amount of oxygen in the exhaust stream. The output
voltage is used by the PCM to adjust the air/fuel ratio of the fuel mixture between a slightly Rich condition and a
slightly Lean condition.
A zirconia-type O
2
sensor provides high output voltage (a Rich condition) and low output voltage (a Lean condition).
A titania-type O
2
sensor changes resistance as the oxygen content of the fuel mixture changes. This results in a low
output voltage (from a Rich condition) and a high output voltage (from a Lean condition). Most Titania O
2
sensors
are found on MFI (Multiport Fuel Injection) systems.
A voltage swing between 100 mV and 900 mV indicates that the O
2
sensor is properly signalling PCM to control the
fuel mixture.
• Symptoms [OBD II DTC’s : P0130 ~ P0147, P0150 ~ P0167]
Feedback Fuel Control System’s (FFCS’s) no entering Closed Loop operation, high emissions, poor fuel economy.
• Test Procedure
1. Connect the shielded test lead to the CH A input and connect the ground lead of the test lead to the sensor
output LO or GND and the test lead probe to the sensor output or HI. (Get the color of the O
2
signal wire or PCM
pin number from a wiring diagram.)
2. Warm the engine and O
2
sensor for 2-3 minutes at 2500 RPM, and let the engine idle for 20 seconds.
3. Rev the engine rapidly five or six times in 2 second intervals from idle to Wide Open Throttle (WOT). Be careful
not to overrev the engine. Engine RPM over about 4000 is not necessary. Just get good snap throttle accels and
full decels.
4. Use the HOLD key to freeze the waveform on the display to check the maximum O
2
voltage, minimum O
2
voltage
and response time from Rich to Lean.
6-3
ABS Sensor-Magnetic
• Theory of Operation
ABS (Anti-lock Brake System) wheel speed sensors generat e AC signals with frequency proport ional t o wheel
speed. The amplitude (peak to peak voltage) increases as the wheel speed increases and is greatly affected by air
gap between the magnetic tip and the reluctor wheel. The ABS computer compares the frequencies and uses this
information to maintain wheel speeds while braking.
This test shows the sensor’s raw output signal or the frequency proportional to wheel speed. The sensor’s output
signal should be continuous as long as the wheel rotates. Spikes or distortion of individual output pulses may
indicate occasional contact between the sensor and the reluctor wheel.
• Symptoms
ABS light on, no ABS signal generation
• Test Procedure
1. Connect the shielded test lead t o the CH A input and connect the ground lead of the test lead to the sensor
output LO or GND and the test lead probe to the sensor output or HI. (Use a wiring diagram for the vehicle being
serviced to get the ABS control unit pin number, or color of the wire for this circuit.)
2. Drive vehicle or spin the wheel by hand to generate signal.
When driving vehicle, back probe the connector leading to the sensor. Place the transmission in drive, and slowly
accelerate the drive wheels.
If the sensor to be tested is on a drive wheel, raise the wheels off the ground to simulate driving conditions. Key
OFF, Engine OFF (KOEO).
3. Use the Glitch Snare mode to detect spikes and dropouts.
4. Compare ABS sensors on all wheels for similarities.
• Reference Waveform
VEHICLE INFORMATION
YEAR
: 1989
MAKE
: Acura
MODEL
: Legend
ENGINE
: 2.7 L
FUELSYS : Multiport Fuel Injection
PCM_PIN : Pos Grn Blu pin 13
Neg Brn pin 18
STATUS
: KOBD (Key On Driven)
RPM
: 1200
ENG_TMP : Operating Temperature
VACUUM : 18 In. Hg
MILEAGE : 69050
6-2
Amplitude and Frequency increase with wheel speed. Output signal should be stable
and repeatable without distorted pulses.
ABS wheel speed sensor
logged while driving 20 MPH
FREQ = 416 Hz
P-P = 3.00 V
