Ignition Systems and Engine Management Sensors/Actuators
What the exam tests
Coil operation, spark timing, sensor signal types and actuator testing.
Core
- Ignition coils store energy in the primary; opening the primary circuit collapses the field and induces high voltage in the secondary. Dwell is the charging time. Coil-on-plug and waste-spark systems differ in secondary path.
- CKP sensors are inductive (two-wire, AC voltage and frequency rising with speed) or Hall (three-wire, square wave switching 0–5 V). CMP sensors time the cam for sequential injection.
- Common sensors: MAP (voltage or frequency), MAF (hot wire/film), TPS/APP (dual potentiometers for plausibility), ECT (NTC resistance falls with temperature), O2 (zirconia narrowband switches 0.1–0.9 V; wideband uses pump current).
- Actuators: injectors (saturated low-impedance or peak-and-hold high-impedance), idle air control, VVT solenoids, electronic throttle.
- Most sensors share a 5 V reference and a sensor ground from the ECU. Do not probe the reference with a test light.
Worked example
A P0335 crank signal code is stored. While cranking, an inductive CKP should produce AC volts that rise with speed, often 0.5–2 V AC; a Hall CKP should switch between about 0.3 V and 4.5 V. If the signal is absent, check the air gap, reluctor, connector and shielded wiring before replacing the sensor. A sensor that produces a signal at the ECU but not at the sensor is a wiring fault.
Traps
Assuming a code names the faulty part; testing a Hall sensor with an ohmmeter only; probing a 5 V reference with a test light; confusing a rich O2 voltage with a lean one; overlooking a bad engine ground.