21/12/2025
หน้าที่ของกล่องประมวลผล ECU สมองของรถ
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🚗 Electronic Injection System Sensors Explained — One by One
📍 Dr.Mechanics | Simple Knowledge for Every Driver
1. MAF – Mass Air Flow Sensor⚡
This sensor measures how much air is entering the intake system.
More air = more fuel.
If the MAF is dirty → engine loses power, fuel economy drops, black smoke may appear.
Common symptoms of a bad MAF:
Poor acceleration
High fuel consumption
Rough idle
Common Fault Codes by Sensor (OBD-II DTC Guide)
MAF – Mass Air Flow Sensor Codes⚡
P0100 – MAF Circuit Malfunction
P0101 – MAF Performance/Range Problem
P0102 – MAF Low Input
P0103 – MAF High Input
P0104 – MAF Intermittent Signal
📌 Dirty MAF = most common cause
2. TPS – Throttle Position Sensor⚡
TPS tells the ECU how much you press the accelerator pedal.
If TPS is faulty → engine idle becomes unstable and RPM jumps.
Bad TPS symptoms:
Hesitation when accelerating
Jerking
High or uneven idle
Common Fault Codes by Sensor (OBD-II DTC Guide
TPS – Throttle Position Sensor Codes⚡
P0120 – TPS Circuit
P0121 – TPS Range/Performance
P0122 – TPS Low Input
P0123 – TPS High Input
P0124 – TPS Intermittent
Unstable idle, hesitation, jerking
3. CKP – Crankshaft Position Sensor⚡
This is the heart of ignition timing.
It tells the ECU the exact crankshaft position so spark and fuel can be delivered correctly.
If CKP fails:
Engine stalls
No start condition
Misfiring
Common Fault Codes by Sensor (OBD-II DTC Guide
CKP – Crankshaft Position Sensor Codes⚡
P0335 – CKP Circuit Malfunction
P0336 – CKP Range/Performance
P0337 – CKP Low Input
P0338 – CKP High Input
P0339 – CKP Intermittent
📌 No-start or sudden engine stall
4. CMP – Camshaft Position Sensor⚡
Works together with CKP.
It helps the ECU control valve timing and fuel injection sequence.
Bad CMP symptoms:
Hard starting
Poor fuel efficiency
Engine stalling
Common Fault Codes by Sensor (OBD-II DTC Guide
CMP – Camshaft Position Sensor Codes
P0340 – CMP Circuit Malfunction
P0341 – CMP Range/Performance
P0342 – CMP Low Input
P0343 – CMP High Input
P0344 – CMP Intermittent
📌 Hard starting & misfire complaints
5. ECT – Engine Coolant Temperature Sensor⚡
This sensor tells ECU engine temperature.
Cold engine = more fuel
Hot engine = less fuel
If faulty: engine may run rich, black smoke, or high fuel consumption.
Common Fault Codes by Sensor (OBD-II DTC Guide
ECT – Engine Coolant Temperature Sensor Codes
P0115 – ECT Circuit Malfunction
P0116 – ECT Range/Performance
P0117 – ECT Low Input
P0118 – ECT High Input
P0119 – ECT Intermittent
📌 Over-fueling when defective
6. O₂ Sensor – Oxygen Sensor⚡
Located in the exhaust.
It checks how much oxygen remains after combustion.
ECU uses this to control air–fuel ratio (14.7:1).
Bad O₂ sensor = low power + high fuel usage.
Common Fault Codes by Sensor (OBD-II DTC Guide
O₂ – Oxygen Sensor Codes
🔻 Upstream Sensor (Bank 1 Sensor 1)
P0130–P0135 – O₂ Sensor Circuit Issues
🔺 Downstream Sensor (Bank 1 Sensor 2)
P0136–P0141 – O₂ Heater/Circuit Issues
📌 High fuel burn + emissions when faulty
7. Fuel Injector⚡
This is the final output device.
ECU decides how long the injector opens based on all sensor inputs.
Long pulse = more fuel
Short pulse = less fuel
Fuel Injector Codes
P0200 – Injector Circuit Malfunction
P0201–P0208 – Injector faults by cylinder
Example:
P0201 = Injector Cylinder 1
P0204 = Injector Cylinder 4
Misfire + cylinder imbalance
⚙️ ECU – The Brain
All sensors report to ECU.
ECU calculates perfect air–fuel mix for power, economy, and emission control.
Common Fault Codes by Sensor (OBD-II DTC Guide
Misfire + cylinder imbalance
🧠 ECU-Related Fault Codes
P0600 – Communication Link Error
P0601 – Internal Control Module Memory
P0603 – ECU Keep Alive Memory Error
P0606 – PCM/ECM Processor Fault
📌 Electrical issues or programming
Why sensors matter?
A modern engine cannot run smoothly without them.
One bad sensor can kill performance and increase fuel cost.
🏁 Dr.mechanics Advice| Quick Diagnostics for Technicians
✔ Clean MAF every 20,000 km
✔ Replace O₂ sensor around 80,000–100,000 km
✔ Diagnose TPS if RPM unstable
✔ Scan codes before replacing parts
✔ Scan live data before replacing
✔ Check wiring & grounds
✔ Don’t ignore intermittent faults
✔ Cheap sensors = more comebacks
