Automotive Service Excellence (ASE) A8 Engine PerformanceIgnition System Diagnosis and RepairMedium
A technician is diagnosing a vehicle with a persistent P0352 (Ignition Coil 'B' Primary/Secondary Circuit Malfunction) trouble code. They have already confirmed power and ground to the coil, and swapped the coil with an adjacent cylinder, but the code remains for cylinder #2. Using an oscilloscope on the control circuit wire for cylinder #2's coil, they observe a constant 12-volt signal with no switching activity from the ECM. What is the most likely cause of this symptom?
- AA short to power in the coil's control circuit wire.
- BExcessive resistance in the coil's secondary winding.
- CAn open circuit in the coil's primary winding.
- DA faulty Engine Control Module (ECM) output driver for cylinder #2.
Show answer & explanationAnswer & explanation
Correct answer: D. A faulty Engine Control Module (ECM) output driver for cylinder #2.
If the control circuit wire shows a constant 12V and no switching, it means the ECM is not providing the necessary ground signal to complete the primary circuit and trigger the coil. Since power and ground to the coil are confirmed, and the coil itself has been swapped, the issue most likely lies with the ECM's internal output driver for that specific cylinder.
Why the other options are wrong
- A. A short to power would keep the circuit constantly powered, but the ECM's job is to ground it, so this signal indicates the ECM isn't doing its job.
- B. Excessive secondary resistance would affect the high voltage output but not the primary control signal from the ECM.
- C. An open primary winding would prevent spark, but wouldn't directly cause the ECM's control signal to be absent or constant 12V.
ECM Ignition Driver Fault
A malfunction within the Engine Control Module (ECM) where the internal circuit responsible for switching an ignition coil's primary circuit fails, preventing spark generation for that cylinder.
- ECM provides the ground/trigger.
- Constant voltage on control wire indicates no switching.
- Often specific to one cylinder's driver.
Memory trick: The 'brain' (ECM) 'commands' the 'spark', if the command is 'stuck', no spark.