PGM-FI Series Part 9 - Final Sensor: What is CKP Sensor? The most important sensor - if it fails, engine won't start at all. No spark fix.
What is CKP Sensor?
CKP = Crankshaft Position Sensor (also called Pulser Coil). Located on left engine cover near stator, facing flywheel magnet reluctor. It generates AC pulse each time crankshaft rotates. Tells ECU: engine RPM and piston Top Dead Center (TDC) position for ignition and injection timing. No CKP = No spark, No fuel.
Function - Why It's The Most Critical
- RPM Signal: ECU calculates engine speed from CKP frequency
- Ignition Timing: ECU fires spark plug at correct moment (e.g., 10° BTDC at idle, 35° BTDC at high RPM)
- Injection Timing: ECU injects fuel at correct crank angle
- Without CKP: ECU doesn't know engine is turning = cuts spark and fuel = engine cranks but won't start
Symptoms of Bad CKP Sensor - Most Searched
1. Engine Cranks But No Spark - Won't Start At All
The #1 symptom. Cranking strong, battery ok, fuel ok, but no spark at plug.
2. MIL Code 8-2 / 9-1 / 19-1
Honda MIL 8-2, 9, or 19 = CKP / Pulser coil circuit failure
3. Intermittent Stalling / Engine Dies When Hot
CKP coil resistance increases when hot = signal drops = engine dies, restarts when cold
4. Weak / Intermittent Spark
5. Tachometer Drops to Zero While Riding
Tacho gets signal from CKP - if drops, CKP failing
How to Test CKP Sensor with Multimeter - The Definitive Test
Resistance Test (Unplugged, Key OFF) - Most Reliable
Find CKP connector: 2 wires (usually Blue/Yellow and Green/White or White/Blue and Green). Measure resistance between them:
- Honda manual bikes typical: 180-300 Ω (CB150R, Sonic 150R, Supra GTR: ~240Ω)
- Below 100Ω or above 500Ω = bad
- Open (OL) = coil broken
- Short to ground: Measure each wire to engine ground - should be OL (open). If continuity = shorted to ground
AC Voltage Test (Cranking)
Set multimeter to AC V 2V. Crank engine (plug out for easier crank). Measure CKP wires while cranking:
- Should produce 0.5-1.5V AC pulse while cranking
- 0V = dead CKP
Air Gap Check
Gap between CKP tip and flywheel reluctor: 0.6-1.0mm. Too wide = weak signal. Check for metal debris on tip.
How to Fix / Replace
- Clean CKP tip and flywheel reluctor from metal dust
- Check wiring: CKP wires often get pinched near stator cover - check for cut
- Replace: Usually sold with stator assembly on some models, but can buy pulser coil separately. Replace gasket, apply small amount of gasket glue
- After replacement, clear MIL code. No calibration needed - just gap check
Related PGM-FI Series - Complete 8 Sensors
Our complete PGM-FI 8-sensor series now complete:
- PGM-FI Overview (all sensors)
- MAP Sensor - Manifold Absolute Pressure
- TP Sensor - Throttle Position
- IAT Sensor - Intake Air Temperature
- EOT Sensor - Engine Oil Temperature
- CKP Sensor - Crankshaft Position (this article - final)
- O2 Sensor & Bank Angle Sensor (bonus)
Labels: Honda Service Guides, Electrical System, Troubleshooting, Engine & Transmission - No Spark Fix