P21BA

Code

Generic P — Powertrain

Cold Start Cylinder 5 Injection Timing

Brand: Generic

Type: P — Powertrain

Views: UK: 29 EN: 38 RU: 33

AI status

Completed

ready

Completed 100%

Page language: EN

Causes

Faulty or clogged fuel injector (cylinder 5)
Injector driver or ECM output fault for cylinder 5
Wiring harness or connector open/short/corrosion to injector 5
Low or unstable fuel rail pressure during cold cranking/start
Incorrect camshaft/crankshaft position (timing belt/chain jumped or sensor fault)
Cold start enrichment strategy fault or ECM calibration/software issue

Symptoms

Rough or difficult cold start focused on initial cranking/start period
Single-cylinder misfire or roughness on cold start (cylinder 5)
White/black/blue smoke on cold start (depending on fuel type and fault)
Check Engine Light (MIL) illuminated, often with freeze-frame data showing low temp/start condition
Poor idle until engine warms up; long cranking times
Reduced cold-start performance or increased fuel consumption until warmed

What to check

Read freeze-frame and stored data; confirm code P21BA and associated live data during cold-start conditions
Inspect injector 5 electrical connector and wiring for corrosion, damage, back-pin plugs and secure fit
Measure injector 5 resistance and compare to specification
Check fuel rail pressure during cranking and cold start with a gauge or scan-tool PID
Observe injector 5 command and feedback (pulse width/duty) with a scope or manufacturer scan tool
Scan for related codes: injector circuit codes, misfire codes, cam/crank sensor codes, fuel pressure codes

Signal parameters

Injector pulse width (ms) for cylinder 5 during cranking/cold start
Commanded injection timing (degrees BTDC/ATDC) during cold start
Fuel rail pressure (bar or psi) during cranking and start
Injector coil resistance/impedance (ohms)
Injector driver current/duty (mA or %)
Crankshaft RPM and crank angle position during cranking

Diagnostic algorithm

Retrieve freeze-frame and live data with scan tool; confirm the code occurs specifically during cold-start conditions and note engine temperatures and rail pressure.
Inspect visually: wiring, pins, connector seals for injector 5. Repair any damaged wiring or corrosion and clear code to retest.
Measure injector 5 resistance and compare to spec. If out of range, replace injector or service as required.
Check fuel rail pressure during cranking and cold start. If low or fluctuating, test fuel pump, pressure regulator, and inlet filter for restriction.
Use an oscilloscope to capture injector 5 waveform and compare to a known-good cylinder. Look for missing pulses, wrong dwell shape, or driver switching issues.
Swap injector 5 with another cylinder (when practical) and re-run cold-start test to see if the code follows the injector. If it follows, replace the injector.
If swapping does not move the fault, backprobe injector driver at ECU to verify driver output. Check for shorts to ground or battery and test driver circuit for proper switching.
Check crankshaft and camshaft position sensors and timing correlation. Repair timing belt/chain or sensors if correlation is incorrect.
If electrical and mechanical checks pass, review ECM software/flash level and cold-start strategy; update ECU calibration if a known issue exists.
After corrective action, clear codes and perform multiple cold-start cycles to confirm repair. If intermittent, consider harness repair or replacement and further ECU testing.

Likely causes

Injector #5 sticking, leaking, or hydraulically clogged
Poor electrical connection or intermittent short to injector 5
Low rail pressure or failing fuel pump/regulator affecting injection timing
Faulty crankshaft or camshaft position sensor causing incorrect timing reference
ECM driver transistor for injector 5 degraded
Cold start sensor inputs (coolant/air temp) incorrect and altering commanded timing