OBD-II Code · Ignition
P2303
Ignition Coil B Primary Control Low
Severity
high
Left alone, this one tends to take other parts with it.
Can you drive it
Not for long
Driving on this one risks further damage. Get it to a shop rather than carrying on with it.
Indicative cost (USD)
$80–$300
Varies by vehicle, diagnosis, parts, and local labor. This is not a repair quote.
Coil B driver circuit low.
How a shop works this
Work from evidence to part, not the other way round. A code names a circuit or a symptom; it does not name the part that failed.
Note every code that is set, not just this one.
Codes that appear together usually narrow the cause faster than any one of them read alone.
Read the freeze frame — the conditions the fault was recorded under.
Cold or warm, idle or load, road speed and engine speed. A fault that only appears cold is a different fault from one that only appears under load, even with the same code on the scanner.
Confirm the fault is current rather than history.
Clear the code and see whether it returns under those same conditions. A code that does not come back may have been logged during a repair, a flat battery, or a bad connection that has since been disturbed.
Then work the likely-causes list in the order shown.
That order is what a shop checks first for this code — wiring and connections before the component they run to, because a connector costs nothing to inspect and is a common answer.
If the code comes back after a repair, the underlying fault is still there. That is the point to bring in a scanner with live data and freeze-frame, or a shop that has one.
Common symptoms
- Misfire cyl 2
- Check engine light
Likely causes
- Wiring shortMost common
- Failed coil
Read the full diagnostic procedureP2303 means the PCM detected a low-voltage condition on the primary control circuit of ignition coil B — the IGT command line to coil B is reading lo…
P2303 means the PCM detected a low-voltage condition on the primary control circuit of ignition coil B — the IGT command line to coil B is reading lower than the expected 0-5V (or 0-12V) reference, or the primary current is below the 5-15A peak the PCM expects during the 2-6 ms dwell.
Cheapest-first ladder
- Inspect the coil B connector for green corrosion, bent or backed-out pins, and chafed wires — connector and harness faults make up the majority of low-side primary codes and cost nothing to find with a flashlight and a pick.
- Ohm the primary winding pin-to-pin — spec is 0.4-1.5 ohms for most COP coils; 0.0 ohms indicates a shorted primary, OL indicates open, either condemns the coil.
- Scope the IGT trigger pulse — clean 0-5V (or 0-12V) square wave with 2-6 ms dwell expected; missing pulse means the PCM driver or harness from PCM to coil is the problem.
- Verify 12V feed pin at the coil with key-on — battery voltage expected; low or absent feed traces back to the ignition relay or fusible link. Expensive-misdiagnosis caveat: swap coil B with an adjacent coil and clear the code — if P2303 follows the coil to the new cylinder, it's the coil; if it stays on the original cylinder, it's the harness, connector, or PCM driver. A $40 coil swap-test saves the $80 misdiagnosis fee for replacing a coil that wasn't the problem.
Vehicle-specific patterns2005-2014 GM LSx V8 (LS1/LS2/LS3, Silverado/Camaro/Corvette) — primary-circuit codes on coils B (typically cylinder 3 or wherever the OEM map assigns…
- 2005-2014GM LSx V8 (LS1/LS2/LS3, Silverado/Camaro/Corvette) — primary-circuit codes on coils B (typically cylinder 3 or wherever the OEM map assigns B on a given platform) are common because the valve-cover-mounted coils take the brunt of exhaust-manifold heat soak.
- 2004-2010Ford 4.6L/5.4L 3V Triton sees P2303 from the same melted/water-intruded connectors that plague all the per-cylinder coil codes on this engine — the COP connector sits in a low spot that collects condensation from the hood lip.
- 2011+Ford 5.0 Coyote (Mustang GT, F-150) sees primary low-side codes from harness chafe where the COP pigtail loops over the intake manifold trim.
- 2007-2018Toyota 2GR-FE 3.5L (Camry/Highlander/Sienna/RAV4) and 2AZ-FE 2.4L generally run 100-150K miles before throwing primary-circuit codes — when they do appear, the failure is usually a single coil rather than a set. Mercedes M271 (1.8L supercharged) and M273 (5.5L V8) coil primaries cluster at 80-120K miles, often with simultaneous failures across multiple cylinders. Common pattern: coil B typically = cylinder 2, 3, or whatever cylinder the OEM firing-order map assigns — verify against the OEM wiring diagram before swap-testing.
Estimated repair$40 (single coil DIY) to $320 (full set on a V8).
Look up another code
P2303 — frequently asked
What does a P2303 code mean?
Coil B driver circuit low.
What causes a P2303 code?
Common causes: Wiring short; Failed coil.
What are the symptoms of a P2303 code?
Typical symptoms: Misfire cyl 2; Check engine light.
Is it safe to drive with a P2303 code?
Not for long. Driving on this one risks further damage. Get it to a shop rather than carrying on with it. Estimated repair: $80-$300.
How do I diagnose a P2303 code?
Work from evidence to part, not the other way round. A code names a circuit or a symptom; it does not name the part that failed. 1. Note every code that is set, not just this one. 2. Read the freeze frame — the conditions the fault was recorded under. 3. Confirm the fault is current rather than history. 4. Then work the likely-causes list in the order shown.
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