Powertrain, generic (extended)

P21BA Cold Start Cylinder 5 Injection Timing

Check engine lightOn

EmissionsRelevant

Drive cycleRequired

Limp modeNo

P21BA can only occur on engines with at least five cylinders – inline fives, V6, V8 and larger. GM's 4.3-litre V6 and 5.3/6.2-litre V8 direct-injection engines use a dual-pulse injection in open loop after a cold start; a GM bulletin explains that the module watches crankshaft speed in this mode and sets P050D (cold start rough idle) if it varies too much. A per-cylinder timing code such as P21BA goes a step further and names the cylinder whose cold-start injection timing missed its target. No manufacturer has published use of P21BA. On which bank cylinder 5 sits depends on the manufacturer's numbering, so check the engine's cylinder layout before testing. Related: P020E (warm), P2B0C (cold-start pulse), P0305.

Likely causes

Injector of cylinder 5 sticking or delivering late when cold

Repair on the wrong injector because of a misread cylinder numbering

Open or high-resistance circuit to injector 5

Symptoms

Check engine light after cold starts
Rough idle during the first seconds after a cold start, possibly together with P050D

Repair estimate

DifficultyHardWorkshop job

Parts and labour€100–1,300

Time0.7–4 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.