Ignition

P1321 — Ignition Coil Power Supply Low, Cylinder 1

Severity: medium Drive with care, to a shop

What P1321 means

The ECM monitors the voltage feeding the cylinder 1 ignition coil through a fuse and relay. If that voltage is too low, the coil cannot build a strong spark. P1321 is most common on Nissan and some other makes, and the exact definition depends on the manufacturer.

Symptoms

  • Cylinder 1 misfire
  • Rough idle and vibration
  • Loss of power and sluggish acceleration
  • Check Engine light on or flashing
  • Often accompanied by P0301
  • Higher fuel consumption

Possible causes

  1. Blown fuse in the coil power feed
  2. Short or open in the coil power wire
  3. Corroded or loose coil connector terminals
  4. Failed cylinder 1 ignition coil
  5. Faulty coil driver inside the ECM
  6. Bad relay or ignition switch problem
  7. Weak engine ground or low system voltage

How to diagnose

  1. Read all codes and freeze frame data, noting any P0301.
  2. Test the battery and charging voltage to rule out a system voltage drop.
  3. Check the ignition coil fuse and relay.
  4. Inspect the cylinder 1 coil connector and harness for chafing, moisture and corrosion.
  5. With the key on, measure supply voltage at the coil connector with a multimeter.
  6. Check the ground and wire continuity to the ECM for opens and shorts.
  7. Swap the coil with another cylinder and see whether the fault follows it.
  8. If power and wiring are good, suspect the ECM coil driver.

Common fixes

  • Replace the blown fuse after finding the cause of the short
  • Repair or replace the damaged wiring section
  • Clean and restore connector and ground contacts
  • Replace the cylinder 1 ignition coil
  • Repair or replace the ECM if its driver has failed

P1321 on different brands

Chevrolet · manuals
The manufacturer describes this code as an Electronic Ignition System fault line.
Chrysler
The code is defined as an Electronic Ignition System fault line.
Hyundai · manuals
Described as an abnormal signal from ignition coil IG.Coil.4.
Suzuki · manuals
Defined as a crankshaft segment malfunction.
VAG
On Audi and VAG vehicles it is listed as knock sensor 3 signal too low.

Questions and answers

What does P1321 mean?

On many makes such as Nissan, it means low supply voltage to the cylinder 1 ignition coil. Other manufacturers define it differently, so check the documentation for your model.

Can I drive with P1321?

Only a short distance to a shop. Misfires harm the catalytic converter and make the engine run poorly.

Where should I start diagnosing it?

Start with the coil power fuse, the cylinder 1 coil connector, and the voltage at that connector with the key on.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.