Input Sensors Study Guide – ASE Prep

Vocabulary flashcards covering key concepts related to input sensors for ASE preparation.

ECT

Engine Coolant Temperature

IAT

Intake Air Temperature

MAP

Manifold Absolute Pressure

TPS

Throttle Position Sensor

APP

Accelerator Pedal Position

MAF

Mass Air Flow

DLC

Data Link Connector

DTC

Diagnostic Trouble Code

HO2S

Heated Oxygen Sensor

CKP

Crankshaft Position Sensor

CMP

Camshaft Position Sensor

KS

Knock Sensor

STFT

Short Term Fuel Trim

LTFT

Long Term Fuel Trim

VSS

Vehicle Speed Sensor

Thermistor

A device that changes resistance with temperature.

Unmetered air

Air entering the engine without passing through the MAF sensor.

Oxygen sensors

Sensors that detect oxygen levels in exhaust gases, types include Zirconia, Titania, and Wideband.

Reference voltage

The voltage supplied to sensors from the PCM.

Zirconia HO2S typical voltage range

0.1V – 0.9V.

Rich mixture

Condition indicated by increased HO2S voltage.

Lean mixture

Condition indicated by decreased HO2S voltage.

Open Loop

PCM does not use O2 sensor data, often during cold starts or faults.

Closed Loop

PCM uses O2 sensor data to control fuel mixture.

TPS voltage at closed throttle

Approximately 0.5V.

TPS voltage at WOT

Approximately 4.5V.

MAP voltage at idle

Approximately 1–2V under high vacuum conditions.

MAP voltage with no engine vacuum

Approximately 4.5–5V at WOT.

Wideband O2 sensors

Provide more precise air-fuel ratio data.

ECT reading of -38°F

Likely indicates a sensor is unplugged or has an open circuit.

PCM function

Monitors systems like AC to adjust idle speed and engine load.

B1S2

Bank 1, Sensor 2 (after catalytic converter).

Upstream

O2 sensor located before the catalytic converter.

Downstream

O2 sensor located after the catalytic converter.

LTFT at +15

PCM is adding fuel, indicating the engine is running lean.

LTFT at -18

PCM is removing fuel, indicating the engine is running rich.

Hot-wire MAF common problem

Contamination from dirt or oil on the wire.

Speed-Density method

Used in systems without a MAF sensor.

GDI engines

Typically use Wideband Oxygen Sensors.

MAP sensors measure

Vacuum levels related to engine load.

ECT effects

Affects fuel mixture, idle speed, cooling fan operation, emissions, and cold start enrichment.

Modern TPS

Often built into the electronic throttle body.

Common reference voltage

5 volts.

MAF g/sec

Grams per second of air.

O2 sensor heaters

Help O2 sensors reach operating temperature quickly.

Disconnected APP sensor effect

Results in loss of throttle response or limp mode.

O2 sensors operating temperature

Need to reach 600°F – 650°F to function correctly.

As engine load increases

MAP voltage increases.

As throttle opens

MAF sensor g/sec, Hz, and voltage all increase.

High LTFT indication

Engine running lean, PCM adds more fuel to correct.