P1309

Ford

Misfire Monitor AICE Chip Fault

Definition source: Manufacturer reference catalog
Definition verification: Not independently verified for display.
Time: Varies by diagnosis and vehicle | Diagnostic difficulty: Medium
Medium Severity

The Ford powertrain control system has detected a fault in the AICE circuitry used by the misfire monitor. That monitor evaluates engine-speed changes to detect misfires. This code points to a problem with the monitoring function; it does not by itself prove the engine is misfiring or that a particular part needs replacement. The misfire monitor may not reliably detect a misfire while this fault is present.

Report an error with this code

⚠️ Before You Begin (Safety First)

This code alone does not usually mean the engine is unsafe to drive. If the check-engine light is flashing, the engine is running very rough, or power drops sharply, stop driving when safe and arrange service; an active misfire can damage the catalytic converter.

Common Symptoms

  • The check-engine light may be on.
  • There may be no noticeable change in how the engine runs because the fault concerns the misfire-monitoring circuitry.
  • Misfire monitoring may be unavailable or unreliable, so a separate misfire may not be detected as expected.
  • Rough running or loss of power can occur if a separate engine misfire is also present; P1309 alone does not establish that.

Common Causes

  • A fault in the PCM's AICE misfire-monitor circuitry.
  • A PCM power, ground, connector or wiring problem that disrupts operation of the monitoring circuitry.
  • A separate engine misfire may coexist, but it is not established by this code.

Diagnostic Steps

  1. Record P1309 and any other stored codes before clearing anything; accompanying codes can help distinguish a monitor fault from an actual engine problem.
  2. Note whether the engine runs rough or the check-engine light flashes. Treat those as signs that a separate misfire may need prompt attention.
  3. With the vehicle off, visually check accessible wiring and connectors for obvious damage, looseness or corrosion. Do not open the PCM or probe terminals without the correct service information.
  4. If the code returns or drivability symptoms are present, have a technician check PCM power, grounds, related wiring and misfire-monitor operation before replacing a control module.

When to Call a Professional

Read all codes and available freeze-frame data, then check for signs of an actual misfire. Verify the PCM's power, grounds, connectors and related wiring before condemning internal PCM circuitry. Follow model-, year- and engine-specific service information to assess the monitor and any applicable module checks.

Compare component listings

Confirm diagnosis and vehicle fitment before buying. A listing does not prove that a part needs replacement. We may earn a commission from qualifying purchases.

Search Amazon Search eBay

Commonly Asked Questions

Does P1309 mean the engine is misfiring?

Not by itself. It identifies a fault in the misfire-monitor AICE circuitry. A real misfire may coexist, so check for other codes and symptoms.

Can I keep driving with P1309?

If the engine runs normally and the check-engine light is steady, arrange diagnosis soon. If the light flashes or the engine runs very rough, stop driving when safe and seek service.

Does this code prove the PCM needs replacement?

No. Wiring, connectors, power or grounds can affect module operation. Those checks come before condemning internal PCM circuitry.

Why might the car have no symptoms?

The fault can affect the monitor rather than engine operation. The vehicle may feel normal even though misfire detection is not functioning reliably.

Browse Available Code Guides

Previous and next available guides in database record order, across makes. Adjacent entries may share a code number and do not necessarily describe related faults.