Powertrain, generic (extended)

P21BC Cold Start Cylinder 7 Injection Timing

Check engine lightOn

EmissionsRelevant

Drive cycleRequired

Limp modeNo

From cylinder 7 on, the code is limited to engines with at least seven cylinders – in practice V8, V10, V12 and W12. Common petrol V8 with direct injection are GM's 5.3- and 6.2-litre small blocks, which a GM bulletin describes with dual-pulse injection after a cold start, and Ford's 5.0-litre Coyote, which since 2018 combines port and direct injection. P21BC reports that during the cold-start heating phase the injection timing of cylinder 7 missed its target; on dual-system engines the direct injector is the part whose timing is shifted. No manufacturer publishes use of P21BC. If the code repeats on cylinder 7 only, test that injector cold and compare it with the others. Related: P021A (warm), P2B0E (cold-start pulse), P0207, P0307.

Likely causes

Direct injector of cylinder 7 slow to open or leaking at low temperature

Chafed or heat-damaged wiring to injector 7

Fault in the high-voltage injector driver of the engine module

Symptoms

Check engine light after cold starts
Rough cold idle, sometimes with P050D or a cylinder 7 misfire code

Repair estimate

DifficultyHardWorkshop job

Parts and labour€120–1,500

Time1–5 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

fuel injectorinjector wiringengine control module

References: law.cornell.edu, static.nhtsa.gov, en.wikipedia.org.