P1368 Ignition Coil D Secondary Circuit
The P1368 code indicates a malfunction in the secondary circuit of ignition coil 'D', which typically corresponds to cylinder 4. The secondary circuit is the high-voltage stage that generates the spark at the spark plug; the ECU monitors feedback from this circuit to confirm that the spark occurred correctly. This code is specific to manufacturers like Honda and Acura, which use individual coil-on-plug (COP) or dual-spark coil systems with supervision resistors. When the engine control module (ECM/PCM) detects an abnormal voltage drop or absence of the firing confirmation signal in the secondary circuit of coil 'D', it sets this fault code and usually turns on the check engine light to protect the catalytic converter from misfire damage.
01. Most Common Causes
- Internally damaged or shorted ignition coil on cylinder 'D'
- Worn, carbon-fouled, or incorrectly gapped spark plug on cylinder 4
- Secondary circuit wiring shorted to ground or open
- Loose, corroded, or oxidized electrical connection at coil 'D'
- Faulty ECM/PCM (rare, but possible if the ignition driver is damaged)
- Electromagnetic interference (EMI) affecting the monitoring circuit
02. Symptoms You Will Notice
- Check Engine Light illuminated
- Engine misfire, rough idle, or hesitation during acceleration
03. Step-by-Step Diagnosis
Scan for codes and verify P1368 is present; check for related misfire codes.
Inspect ignition coil 'D' and its connector for damage, corrosion, or loose fit.
Test coil 'D' primary and secondary resistance with a multimeter and compare to specs.
Remove and inspect spark plug on cylinder 4 for wear, fouling, or incorrect gap; replace if needed.
Check wiring between coil 'D' and ECM for shorts, opens, or high resistance.
If all else passes, perform a swap test with a known-good coil to rule out coil failure.
As a last resort, test ECM ignition driver output or replace ECM if confirmed faulty.
1. Frequently Asked Questions
Is it safe to drive?▼
No, it is not safe to drive with this code. The misfire can damage the catalytic converter and cause poor engine performance. Have the vehicle diagnosed and repaired promptly.
How much does it cost to fix?▼
The cost typically ranges from $150 to $400, including parts (ignition coil and possibly spark plug) and labor. Diagnostic fees may add $50-$100.