P0321

P0321 indicates the ignition or distributor engine speed input is out of expected range or performance — meaning the signal is present but the frequency, amplitude, or pattern doesn't match what the ECM expects. This is more diagnostic-sensitive than P0320 (no signal) or P0322 because intermittent signal degradation can come from many sources: a partially failed sensor putting out a weak signal, a damaged reluctor tooth on the crank tone wheel, a worn timing chain stretching the crank-to-cam relationship past the learned correlation window, or harness shielding failure letting alternator/coil noise corrupt the signal. Start with a scope on the CKP signal at cranking and idle — a healthy magnetic pickup sweeps from about 0.5V peak-to-peak at cranking up to 80V+ at redline; a Hall-effect 3-wire should produce a clean 0-5V square wave with consistent duty cycle. Caveat: aftermarket lightweight underdrive pulleys without proper reluctor alignment will throw P0321 from day one; verify pulley OEM-spec before chasing sensor parts.

Vehicle-specific patterns: BMW M54/M52TU inline-6 (E46 330i, E39 530i, E60 525/530i, 1999-2006) — stretched timing chain plus worn guides cause CKP-to-CMP correlation drift, P0321 with hot-start hesitation; replace chain, guides, and tensioner as a kit ($400-700 parts, 8-12 hr labor). Toyota 2GR-FE V6 (Camry, Avalon, RAV4, 2007-2017) — VVT-i actuator wear creates intermittent P0321 paired with cold-start rattle. GM 3.6L LY7/LLT V6 (CTS, Acadia, Traverse, 2007-2011) — timing chain stretch is the signature on this engine family by 100K miles. Nissan VQ35DE V6 (Maxima, Altima, Murano, 350Z, 2002-2008) — failed CKP sensor producing weak signal at hot operating temp; sensor is $60-90 part on the bellhousing. Estimated repair: $80 to $1,800.