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Autopapyrus · BYD F3 1.5 (2007)
https://autopapyrus.com/guides/byd/f3/engine-management-system-diagnostics/
Compiled automatically from service literature and owner experience. Specs are for the typical configuration — check them against your exact car before you start.

BYD F3 1.5 (2007): Engine Management System Diagnostics

The 1.5 engine (4G15S, 16 valves) is controlled by a Bosch control unit with multi-port fuel injection and a distributorless ignition system. Diagnostics move from reading the codes and data from the control unit to checking the sensors, ignition, fuel system and air intake path.

Difficulty: Medium Time: 1-2 hours Steps: 13

Parts

11
№PartAlternatives
01 Crankshaft position sensorif faulty
02 Camshaft position sensorif faulty
03 Engine coolant temperature sensorif faulty
04 Throttle position sensorif faulty
05 Manifold absolute pressure (MAP) sensorif faulty
06 Oxygen sensor (lambda sensor)if faulty
07 Idle air control valveif faulty
08 Ignition coilsif faulty
09 Spark plugsif faulty Bosch, NGK, Denso
10 Fuel injectorsif faulty
11 Fuel filterif faulty Bosch, NGK, Denso

Tools

7
  • OBD-II scanner (or ELM327 adapter with software)
  • multimeter
  • fuel pressure gauge
  • socket set
  • spark plug socket
  • throttle body cleaner
  • oscilloscope or test light if needed

Step by step

13 steps
  1. Describe the symptom: no start, unstable idle, hesitation, increased fuel consumption, Check Engine light on. Note when it occurs: on a cold or warm engine, under load or at idle.
  2. Check the basic condition: battery charge (at least 12.4 V with the engine off, 13.5-14.5 V with the engine running), clean terminals, secure ground wires on the body and engine, and the fuses and relays in the engine compartment fuse box.
  3. Connect the scanner to the diagnostic connector under the dashboard, to the left of the driver. Turn the ignition on and read the fault codes, including stored and pending codes. Record the codes and freeze frame data, and only then clear them.
  4. If the scanner cannot communicate with the control unit, check the power at the connector (positive on pin 16, ground on pins 4 and 5), the diagnostic fuse and the power supply to the control unit.
  5. Evaluate the live data on a warm engine: coolant temperature 85-95 °C, idle speed roughly 750-850 rpm, oxygen sensor readings should oscillate periodically, and fuel trims within about ±10%. Values outside these ranges point to an air leak, a fuel problem or faulty sensors.
  6. Check the air intake path: the condition of the intake boot after the air flow meter or sensor, clamp tightness, the brake booster and crankcase ventilation hoses, and the cleanliness of the throttle body and idle air control valve. An air leak causes an unstable idle and a lean mixture.
  7. Check the ignition: remove the spark plugs and inspect them (carbon deposits, oil, gap about 0.8-1.0 mm, exact value per the service manual), check the coils and spark plug wires, and if necessary swap the coils between cylinders to see whether the misfire moves to another cylinder.
  8. Check the fuel system: fuel rail pressure with the ignition on and at idle, whether the system holds pressure after the ignition is turned off, and the operation of the fuel pump (you should hear it hum for 2-3 seconds after the ignition is turned on). Compare the pressure value with the specification for this engine. Assess the condition of the fuel filter and the operation of the injectors (listening with a stethoscope, coil winding resistance).
  9. Check the sensors with a multimeter: the resistance of the coolant temperature sensor should change smoothly as the engine warms up, the throttle position sensor should give a smooth voltage change without jumps, and the crankshaft sensor should have an intact winding and an undamaged air gap to the pulley. The sensor reference supply is 5 V.
  10. If there are sensor codes, check its circuit: the connector (corrosion, pushed-out pins), the wiring to the control unit for opens and shorts to ground, and only then replace the sensor.
  11. Check the mechanical condition: cylinder compression (variation between cylinders no more than 10-15%), the timing marks and the condition of the belt, and whether the catalytic converter is clogged (loss of power, overheating).
  12. After fixing the cause, clear the codes, warm up the engine, take a test drive and read the fault memory again. If the code returns, continue diagnostics along the same circuit.
  13. Tightening torques when removing parts: spark plugs usually 20-25 N·m (15-18 lb-ft), sensors and coils are secured with small bolts at 8-12 N·m (6-9 lb-ft) (exact values per the manufacturer's specification). Do not overtighten threads in aluminum parts.

Common mistakes and warnings

  • Do not disconnect the control unit or sensor connectors with the ignition on
  • Do not replace parts at random based on a single error code: the code points to a circuit, not necessarily to a faulty sensor
  • Perform work on the fuel system away from open flames and after relieving the fuel rail pressure
  • If you lack experience or need a diagnostic bench to test the control unit, contact a specialist repair shop