P2308 Code Fix: Ignition Coil C Secondary Circuit
P2308 Code: Check the Plug and Boot Before Replacing Coil C
P2308 concerns the high-voltage side of ignition coil C. A worn plug, carbon-tracked boot or oil-filled plug well can overload a healthy coil.
P2308 = Ignition Coil C Secondary Circuit. P2308 means the control module detected abnormal behavior in ignition coil C secondary output. Verify which cylinder the manufacturer calls coil C, inspect the plug and boot, then compare coil output and misfire data.
What Does P2308 Actually Mean?
P2308 means Ignition Coil C Secondary Circuit. The secondary circuit is the high-voltage path through the coil, boot or lead, spark plug and combustion gap. The module inferred that coil C output did not behave normally.
The previous draft called this a coil B primary/secondary fault on cylinder 2. Both details are wrong. Coil C often corresponds to the third cylinder in a simple sequential layout, but firing order and manufacturer naming can change the mapping. Confirm the coil-C cylinder in service information before moving parts.
- FCA 3.6L ignition-system service communication
- Workshop DTC reference listing P2308 as Coil C secondary circuit
Always use the service information for the exact VIN; thresholds and test sequences differ by manufacturer.
Symptoms of P2308
The light may flash when coil C misfires under load.
A P030x code often identifies the affected cylinder.
The cylinder may fire intermittently or stop.
High cylinder pressure exposes weak secondary insulation.
Incomplete combustion increases cranking time and fuel use.
Visible or audible leakage can occur around a damaged boot.
What Causes P2308? (Ranked Cheapest First)
The labels and order below are diagnostic weightings for test sequence, not published failure-rate statistics. Vehicle design, mileage and companion codes can change the ranking.
Worn, fouled or incorrectly gapped spark plug (Most common diagnostic weighting)
A wide or contaminated gap raises firing voltage and overloads the secondary circuit.
How to prove it: Remove the coil-C plug, inspect it and measure the gap against specification.
$10-$180Carbon-tracked boot, cracked insulator or oil-filled plug well (Common diagnostic weighting)
Secondary voltage leaks to ground before it crosses the spark-plug gap.
How to prove it: Inspect in bright light for black tracking lines, moisture, oil and torn rubber.
$10-$350Weak or internally damaged ignition coil C (Common diagnostic weighting)
Heat and repeated high firing voltage break down the coil winding or insulation.
How to prove it: Swap with a known-good cylinder when allowed and see whether the fault follows.
$40-$300Coil connector, power feed or ground fault (Occasional diagnostic weighting)
A poor primary supply can create weak secondary output even though P2308 names the secondary side.
How to prove it: Load-test coil power and ground and inspect terminal tension.
$0-$400Injector, compression or mixture problem (Occasional diagnostic weighting)
A non-ignition misfire can make the PCM flag secondary behavior that looks abnormal.
How to prove it: If the code stays on the cylinder after a coil and plug swap, test injector and compression.
$80-$3,000PCM coil driver or calibration problem (Rare diagnostic weighting)
Module failure is possible after the plug, boot, coil and external circuit pass.
How to prove it: Verify the control pattern at the PCM and check bulletins before replacement.
$300-$2,000What You'll Need
Diagnostic tools
- Full-system scan tool with misfire counters
- Adjustable spark tester
- Digital multimeter and back-probes
- Spark-plug socket and gap gauge
- Compression tester if the misfire stays
Possible parts and supplies
- Correct spark plug for the engine
- Coil boot and spring if serviceable
- Ignition coil C only after testing
- Valve-cover seal if oil entered the plug well
iCarzone UR1000 Bidirectional Scan Tool with ECU Coding
Identify the companion misfire, graph cylinder counters and load, run supported coil cut-out tests and save freeze frame before swapping coil C parts.
How to Diagnose P2308 at Home
-
1
Identify coil C and save companion codes
The letter does not guarantee a universal cylinder number.
- Record P2308, every P030x code and freeze-frame load.
- Use the firing order and service diagram to map coil C.
- Check whether the code appears only under boost or heavy load.
- Do not move a coil until its original position is documented.
-
2
Inspect the plug well, boot and spark plug
The secondary path is the first place to look.
- Remove coil C after the engine cools.
- Check for oil, coolant, water and carbon tracking in the well.
- Inspect the boot spring and coil tower for corrosion.
- Measure spark-plug gap and replace a damaged or fouled plug.
-
3
Compare coil output and perform a controlled swap
A failed coil should carry the fault to its new location.
- Use an adjustable spark tester with the approved gap.
- Compare coil C output with a known-good coil.
- Swap coils only if the manufacturer allows it.
- Clear codes and see whether the secondary or misfire fault follows.
-
4
Load-test coil power, ground and control
A healthy coil still needs a stable primary supply.
- Check battery and charging voltage first.
- Measure coil supply voltage under load.
- Inspect connector pin tension and ground voltage drop.
- Check the control pattern with an appropriate meter or scope.
-
5
Test injector and compression if the fault stays
A cylinder problem can remain after ignition parts move.
- Compare injector command and balance where supported.
- Inspect for a vacuum leak near the affected runner.
- Measure compression and perform leak-down if needed.
- Repair the cylinder fault rather than fitting another coil.
-
6
Repair and verify under load
P2308 often returns only when firing voltage rises.
- Install the correct plug, boot, coil or wiring repair.
- Torque the plug and coil fasteners to specification.
- Repeat the original load condition while watching misfire counts.
- Confirm no arcing, flashing warning or returning code.
Safety: Ignition coils generate dangerous voltage. Use insulated tools and an approved spark tester, and never hold a coil or lead while the engine runs.
How Much Does P2308 Cost to Fix?
| Repair | DIY Cost | Shop Cost | Notes | Type |
|---|---|---|---|---|
| Spark plug inspection or replacement | $10-$80 | $100-$250 | Start here | DIY/Inspect |
| Coil boot or plug-well seal | $10-$120 | $120-$350 | Common | DIY/Inspect |
| Ignition coil C | $40-$180 | $150-$450 | Swap-test | DIY/Inspect |
| Connector or harness repair | $10-$100 | $150-$450 | Load-test | DIY/Inspect |
| Injector or compression diagnosis | $40-$300 | $200-$900 | If fault stays | Shop |
| Internal-engine or PCM repair | N/A | $800-$3,500 | Last resort | Shop |
Prices are broad U.S. estimates for July 2026. Labor rate, access and parts availability can move the final bill substantially.
Which Vehicles Commonly Report P2308?
| Make / Model | Years | Powertrain | Diagnostic Notes | Focus |
|---|---|---|---|---|
| Chrysler, Dodge, Jeep and Ram | 2011-2024 | 3.6L Pentastar and other gas engines | Confirm coil-C mapping and inspect plug-well oil or connector fit. | High |
| Mercedes-Benz | 2008-2024 | Gas engines | Secondary-circuit codes can appear under load with worn plugs. | High |
| Volkswagen and Audi | 2008-2020 | TSI/TFSI | Plug gap and coil-boot tracking deserve early inspection. | Medium |
| Mazda | 2007-2022 | Gas engines | Use firing-order data rather than assuming coil C equals cylinder 3. | Medium |
| Kia and Hyundai | 2011-2023 | Gas engines | Coil connector and plug condition are common test points. | Medium |
| Other coil-on-plug vehicles | 2005-2024 | Gas engines | Manufacturer mapping and detection strategy vary. | Lower |
Pentastar V6 applications
A coil swap can identify an internal coil fault, but oil in the plug well and a worn plug can damage the replacement. Inspect and correct the leak or excessive gap before installing a new coil.
Turbocharged engines
Higher cylinder pressure under boost demands more firing voltage. A marginal plug gap or carbon-tracked boot can idle normally and fail only during acceleration, so verification must repeat the original load.
Should You DIY or Call a Mechanic?
- ✓ You can map coil C from the firing order.
- ✓ The plug and coil are accessible.
- ✓ You have an approved spark tester and insulated tools.
- ✓ The engine does not have a flashing warning at idle.
- → The check-engine light flashes or the engine shakes heavily.
- → The plug is seized or damaged in the cylinder head.
- → The fault stays after plug and coil swaps.
- → Compression, injector or PCM testing is required.
Frequently Asked Questions
What does P2308 mean?
Is P2308 coil B or coil C?
Does coil C always mean cylinder 3?
Can a spark plug cause P2308?
Should I replace the coil first?
How does the UR1000 help?
Can I drive with P2308?
How do I verify the repair?
This article is for informational purposes only. Always follow the factory service manual, safety procedures and local emissions rules for the exact vehicle. iCARZONE is not responsible for damage caused by improper diagnosis or repair.
- Tags: Diagnostic Guide OBD-II P2308 UR1000