P21BB

Code

Generic P — Powertrain

Cold Start Cylinder 6 Injection Timing

Brand: Generic

Type: P — Powertrain

Views: UK: 30 EN: 35 RU: 34

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Page language: EN

Causes

Faulty or sticking injector (cylinder 6)
Open, shorted or intermittent wiring or connector to injector driver for cylinder 6
Poor ground or supply voltage to injector driver circuit
Faulty injector driver output in the powertrain control module (PCM/ECM)
Low or unstable fuel rail pressure (especially at cold start)
Faulty crankshaft or camshaft position sensor or loss of cam/crank synchronization

Symptoms

Hard starting or extended cranking when engine is cold
Rough idle or misfire immediately after cold start on cylinder 6
Increased white/black smoke or unusual exhaust odor on startup
Illuminated malfunction indicator lamp (MIL/Check Engine) with P21BB stored
Possible reduced cold-start performance or limp-home behavior

What to check

Read stored codes and freeze-frame or snapshot data to confirm conditions when P21BB set
Check for additional related codes (injector circuits, cam/crank sensors, fuel pressure)
Inspect injector connector and wiring for damage, corrosion, pin push-out, or poor pins
Measure injector supply voltage and ground at connector with key on/crank
Compare commanded injection timing/pulse width for cylinder 6 to other cylinders using scan tool live data
Monitor fuel rail pressure during cranking/cold start

Signal parameters

Commanded injector pulse width (ms) for cylinder 6 — should be within expected range for temperature/load and match other cylinders within tolerance
Injector driver switching voltage: supply typically ~12 V and driver switches to ground (verify with multimeter/oscilloscope)
Injector coil resistance: low-ohm solenoid type (refer to OEM spec); unusually high/low resistance indicates fault
Injector driver waveform shape and timing relative to crank/cam position — clean switching edges, expected dwell and pulse timing
Fuel rail pressure during cranking: should meet cold-start pressure targets per vehicle specification

Diagnostic algorithm

Retrieve and record trouble codes, freeze-frame data and live PID values during a cold-start attempt.
Visually inspect wiring and connector for cylinder 6 injector. Repair any damaged wiring or poor connector terminals.
Check supply voltage and ground at the injector connector with key on and during cranking.
Compare the commanded pulse width / injection timing for cylinder 6 to the other cylinders using a scan tool; note discrepancies.
Measure injector coil resistance; if out of spec, replace injector. If in spec, perform injector bench or on-vehicle activation test.
Use an oscilloscope to capture the injector driver waveform on cylinder 6 and compare to a known-good cylinder. Look for missing pulses, excessive dwell, or distorted waveforms.
Check fuel rail pressure and regulator operation during cold start; repair low/high pressure faults and retest.
Verify crankshaft and camshaft position sensor signals and cam/crank sync (timing). Repair or replace sensor or correct timing if out of spec.
If problem follows the injector when swapped to another cylinder, replace the injector. If it stays with the wiring/connector, repair the wiring or PCM driver as indicated.
After repairs, clear codes and perform multiple cold-start cycles and road tests to confirm the fault does not return. Re-scan for related codes.

Likely causes

Defective injector solenoid or nozzle on cylinder 6
Wiring harness damage or poor connector contact to cylinder 6 injector
Injector driver fault in the PCM (less common than wiring/injector)
Low fuel pressure or faulty pressure regulator affecting injection timing during cranking
Faulty cam/crank position sensor producing incorrect timing reference at cold start

Fault status

⚠️ Status

Cold start injection timing for cylinder 6 outside allowed parameters — ECM detected incorrect or missing injection event during cold start for cylinder 6.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0-3.0 hours

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