Is P1000 actually a fault?

No. P1000 is not a fault code — it's an informational status. It means the OBD system has not yet completed its self-diagnostic tests. It will clear automatically after the ECU completes its check cycle, usually within 50–100 miles of driving.

Will P1000 cause an MOT fail?

Yes. An MOT OBD scan shows readiness status. If P1000 (or any readiness monitor) is incomplete, the test will fail even if there are no actual faults. This is why it's important to complete a drive cycle after battery disconnection before an MOT.

How long does it take to clear P1000?

Usually 50–150 miles of varied driving. The ECU needs to run all its diagnostic tests under different engine states: cold, warm, idle, cruise, and acceleration. City driving with hills is faster than motorway cruising.

Why does battery disconnection trigger P1000?

The readiness status is stored in the ECU's volatile memory. When power is cut, this memory is cleared, so the ECU must re-run all its tests to confirm the car is still healthy before it marks the readiness monitors as complete.

Will this fault code cause my car to fail its MOT?

It depends on which warning light the code is triggering. Since 2018, any car presenting with an illuminated amber Engine Management Light (EML) at the MOT is a Major failure under DVSA rules — even if the car drives perfectly. A red warning light is always a Major or Dangerous failure depending on context. If clearing the fault makes the light go out and the code does not reappear during the pre-test drive, you will pass; if the code returns within minutes of clearing, the underlying fault must be fixed before MOT day. A tester is required to fail the car on the light being on, regardless of whether the underlying fault is something safety-critical or not. For codes that affect emissions specifically (catalyst, lambda, EGR), the car may also fail the actual emissions check. Fix the cause, clear the code, and drive the car for a few miles before the test.

P1000 — OBD System Readiness Test Not Complete

What Is P1000?

P1000 is not a fault code in the traditional sense — it's an informational status. It means the engine control unit has not yet completed its built-in self-diagnostic tests (called "readiness monitors"). The OBD system runs continuous checks on the emissions systems, oxygen sensors, catalyst efficiency, and other components. When you disconnect the battery or clear fault codes, the ECU resets these checks and must run them again to confirm the car is operating normally.

Once the ECU completes all its tests under various driving conditions (idle, acceleration, steady cruising, cold start), it marks the readiness monitors as "complete" and P1000 disappears. This usually takes 50–150 miles of normal driving.

Common Symptoms

An OBD scanner shows P1000 but no other faults
The engine runs normally — no drivability issues at all
MOT OBD test reports "Readiness monitors not complete" and fails
Code appeared after battery disconnection or code clearing
Dashboard check engine light may or may not be illuminated
Everything about the car's performance is perfectly normal

Common Causes

Battery DisconnectedRemoving the negative terminal resets the readiness monitor memory. ECU must re-run tests.

Fault Codes ClearedClearing codes with a scanner also resets the readiness status to "incomplete".

Alternator ReplacementDisconnecting the battery during alternator work triggers the same reset.

Recent Engine WorkAny work requiring battery disconnection (spark plugs, belts, etc.) resets the monitors.

ECU ReprogrammingIf the ECU has been updated or reprogrammed, all monitors reset.

Very New VehicleBrand new cars may show P1000 until the first 100–200 miles are driven.

How to Diagnose P1000

Confirm No Real Faults

Connect an OBD scanner and read all fault codes. If P1000 is the only code present and no other faults are logged, P1000 is simply a readiness status issue — not a mechanical problem. The car is safe to drive. If other faults are present, address those first.

Check Readiness Monitors

Most OBD scanners show a "Readiness" section listing individual monitors: Oxygen Sensor, Catalyst, EGR, EVAP, Thermostat, etc. If all show "Not Ready" or "Incomplete", this confirms P1000 is just a status — the car hasn't completed its drive cycle yet. If several monitors show "Ready" and only one or two are incomplete, the ECU will finish within a few more miles.

Drive With Varied Conditions

To complete the readiness monitors quickly, vary your driving: start the engine cold (don't warm it up first), drive at steady speed on a motorway for 10–15 minutes, then drive through city streets with acceleration and deceleration. Include at least one full throttle acceleration from a stop. This exposes the engine to all the conditions the ECU tests.

Re-scan After 50 Miles

Drive the car normally for 50–100 miles, covering varied roads (city, motorway, hills if possible). Then scan again with your OBD tool. Most monitors should now show "Ready". If all monitors are ready and P1000 is gone, the readiness cycle is complete. If some are still incomplete, drive another 50 miles and check again.

MOT: Complete Before Testing

If you have an MOT coming up, ensure the readiness monitors are complete before you go. Schedule your MOT for at least 100–150 miles after battery work or code clearing. If P1000 appears at MOT, the test will fail immediately. Reschedule after completing a proper drive cycle.

Note:P1000 is often misunderstood as a fault, especially by MOT testers unfamiliar with readiness monitors. You are not required to repair anything — simply drive the car normally for a few days and the monitors will complete on their own.

Verdict

P1000 is not a fault — it's a non-issue that resolves automatically. After disconnecting the battery, clearing codes, or replacing the alternator, simply drive the car normally for 50–150 miles with varied speed and acceleration. The ECU will complete its self-checks and P1000 will disappear. If an MOT is approaching, give yourself at least a week of normal driving after battery work to ensure readiness is complete. There's nothing to repair, no part to replace, and no danger — your car is running perfectly fine.