Code
P1335
HUMMER
P — Powertrain
CKP Circuit
AI status
Completed
Completed
100%
Causes
- Damaged or failed crankshaft position (CKP) sensor
- Open, shorted, or corroded wiring/connector in CKP circuit
- Poor sensor air gap or damaged reluctor/trigger wheel/tooth
- Loose or missing sensor mounting or incorrect sensor alignment
- Faulty PCM or poor PCM connector/ground
- Intermittent connection from vibration (broken wire/frayed harness)
Symptoms
- Malfunction Indicator Lamp (MIL/CEL) illuminated
- Engine cranks but will not start or starts intermittently
- Stalling immediately after start or while driving
- Rough idle, misfire or poor acceleration
- RPM signal missing or erratic on scan tool
- No or irregular crankshaft position waveform on oscilloscope
What to check
- Retrieve freeze-frame data and all stored codes with a scan tool; note related cam/crank codes
- Attempt to start while monitoring CKP PID and rpm on a scan tool
- Visually inspect CKP sensor, connector, wiring harness and reluctor/trigger wheel for damage, oil, or debris
- Check battery voltage and engine grounds (negative battery to engine/PCM)
- Backprobe sensor connector to verify reference voltage/power/ground and signal while cranking
- Measure sensor resistance and continuity of harness to PCM (compare to service specifications)
Signal parameters
- Passive/magnetic CKP: AC sine/sinusoidal waveform; AC amplitude increases with engine speed (no steady DC). Resistance typically in the hundreds of ohms (refer to vehicle spec).
- Active/Hall-effect CKP: square wave 0–5V (or 0–12V on some older designs) with frequency proportional to engine speed; requires 5V reference and ground from PCM.
- Typical test conditions: while cranking or idling expect consistent pulse train; frequency = pulses per crank revolution × RPM/60. Use oscilloscope for waveform integrity, frequency, amplitude, and symmetry.
- If signal is absent, measure for reference voltage (if applicable) and ground at sensor — reference should be stable near vehicle specification (usually ~5V for Hall sensors).
Diagnostic algorithm
- Read and record P1335 plus any related codes and freeze-frame data. Note operating conditions when fault occurred.
- Inspect battery, charging system, and engine grounds. Restore good battery voltage and grounds before further testing.
- Visual inspection: check CKP sensor, connector, wire harness, and reluctor/trigger wheel for damage, oil contamination, magnetization, or debris. Repair physical damage.
- Backprobe the sensor connector. With key on/cranking, verify reference power (if Hall-type), ground, and check for a signal on the output lead using a digital multimeter (frequency) or oscilloscope (waveform).
- If no signal, check continuity from sensor connector to PCM connector and inspect for opens/shorts to battery or ground. Repair any wiring faults.
- Measure sensor resistance (for passive sensors) and compare to spec; replace sensor if out of range. For active sensors, substitute a known-good sensor if available.
- Inspect reluctor/trigger wheel for missing/bent teeth, excessive runout, or timing-chain/belt jumps that may cause incorrect timing signals.
- After repairs, clear codes and attempt to start; monitor CKP signal and related PIDs while cranking and idling. Confirm code does not return during test drive.
- If wiring and sensor check good but problem persists, test PCM input circuit and grounds; replace PCM only after ruling out sensor and wiring faults. Record all test results.
- Safety note: disconnect battery when repairing wiring; take care around rotating engine parts when checking air gaps or start/crank testing.
Likely causes
- Failed CKP sensor (most common)
- Damaged wiring or corroded connector at sensor or PCM
- Reluctor/trigger wheel damage or excessive sensor gap
- PCM input circuit fault or poor ground
Fault status
Status
P1335 — Crankshaft Position (CKP) Circuit: PCM detected an abnormal/crankshaft position sensor signal (open, short, missing, intermittent or out-of-range).
Repair difficulty: Medium
Diagnostic time: 1.0 - 3.0 hours
Similar codes
Repair manuals
Manual library for HUMMER
138
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