P21BA: Cold Start Cylinder 5 Injection Timing

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.

Cylinder 5 is numbered according to the manufacturer: check your engine's manual before working on it.

Symptoms

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

Most 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

What to check, in order

Start with the simplest. You can tick off each step.

1. Check the connector and wiring of the injector indicated
2. Measure the resistance and compare it with the manufacturer's specification
3. Check the control signal with an oscilloscope; on direct injection or diesel engines, leave this to a repair shop because of the high voltages
4. On diesels, check the per-cylinder injection corrections

Good to know

• Repair difficulty: hard
• It affects emissions.

What each character of P21BA means

• P: Powertrain: engine and transmission
• 2: Generic code: same on every make
• 1: Air and fuel
• BA: Specific fault in that system

Frequently asked questions

Can I keep driving with code P21BA?

Drive as little as possible and go to a repair shop. If you smell fuel or the engine is shaking badly, do not keep driving.

What causes code P21BA?

The most common causes are: 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.

Related codes

• P21B9Cold Start Cylinder 4 Injection Timing
• P21BBCold Start Cylinder 6 Injection Timing
• P020ECylinder 5 Injection Timing
• P2B0CCold Start Cylinder 5 Injection Pulse Performance
• P0205Cylinder 5 Injector A Circuit/Open
• P0305Cylinder 5 Misfire Detected
• P050DCold Start Rough Idle

Sources

• law.cornell.edu: 13 CCR 1968.2
• static.nhtsa.gov: MC 10143438 9999
• en.wikipedia.org: Ford EcoBoost engine

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.