Crank & cam signal checks (no scope needed)

A lot of people replace crank/cam sensors because a code mentioned them. Before you do, use these fast sanity checks. You can often prove the issue is wiring, power/ground, or mechanical timing without a scope.

Start with the question: does the ECU “see” the engine?

Watch RPM while cranking (scan tool). If it stays at 0, the ECU is not seeing a crank signal (or it cannot process it).
If you do get RPM, crank signal is likely present. Now focus on sync (cam) or timing, not “no signal”.

Common symptoms

Crank-no-start, starts then dies
Random cut-out over bumps / heat
Extended crank, backfire, rough idle after starting
Codes like P0335/P0340, correlation/sync faults

Don’t assume

A sensor is bad because a code names it
"New sensor" means “fixed” (many are poor quality)
Correlation codes always mean a stretched chain (often oil/VVT/wiring)

Fast checks you can do with a multimeter

Power and ground at the sensor (back-probe if possible). Many failures are broken ground, corroded splice, or missing feed.
Connector condition: oil ingress, green corrosion, stretched pins, damaged shielding on the loom.
Reference voltage shorts: if it’s a 3‑wire hall sensor, confirm the 5V reference is present and stable.

Shortcut: If you have multiple weird sensor codes at once, check the shared 5V reference and sensor grounds first. See: 5V reference & sensor grounds.

Scan-tool clues that point away from the sensor

RPM signal present but still no start → check fuel pressure, spark, immobiliser, and sync status.
Sync / correlation flags changing with RPM/temperature → suspect wiring/connector movement, VVT control, or oil issues.
Misfires + correlation after timing work → suspect mechanical timing alignment, tone ring damage, or incorrect sensor gap.

When to suspect mechanical timing

Correlation/sync faults can be genuine. Before committing to a strip-down, do the “cheap” checks:

Oil level/condition and correct grade (VVT is oil-hydraulic)
VVT solenoid tests and commanded vs actual cam angle (if available)
Listen for chain rattle on cold start; review service history