4A54

What Code 4A54 Means

Code 4A54 points to a fault in the activation circuit for the cylinder 2 glow plug. The pre-start heating system is controlled by the engine control unit (DME), which supplies voltage to the glow plug through a power module or relay. The code sets when the DME detects a deviation in circuit operation: an open circuit, a short, or a mismatch in current draw.

Glow plugs are needed for reliable cold-weather starting of a diesel engine, preheating the combustion chamber. The fault can come from the glow plug itself (wear, broken element), damaged wiring or connectors, or a faulty glow plug control module.

Symptoms

• Hard starting (long crank) in cold weather.
• Rough running after a cold start (misfires, shaking).
• A possible fault message on the instrument cluster (depending on equipment).

Diagnosis and Repair

1. Read the fault codes with diagnostic equipment (ISTA, INPA) and confirm that code 4A54 is active or stored.
2. Check the cylinder 2 glow plug: measure the plug's resistance with a multimeter. Resistance should match the manufacturer's spec (usually under 1 ohm). An open circuit or a significant deviation points to a bad plug.
3. Check the wiring and connectors: inspect the harness running to the plug for damage, corrosion, and loose contacts. Check circuit continuity from the control module to the plug.
4. Check the glow plug control module (if a separate module is fitted): confirm it has no faults, and check its power and control signals.
5. Replace the faulty glow plug once its failure is confirmed. Use genuine (OE) BMW parts or quality equivalents that meet spec.
6. Clear the codes and take a test drive to confirm the fault doesn't return.

Secondary Problems

Running for a long time with a faulty cylinder 2 glow plug can lead to:

• Hard starting and added wear on the starter motor and battery.
• Rough running, extra vibration and noise, especially when cold.
• Higher emissions and lower combustion efficiency.
• Possible catalytic converter damage from unburned fuel.
• Risk of damage to the glow plug control module if the circuit shorts.

Fix the fault as soon as possible to avoid more serious consequences.