P1243

Fuel Pump Secondary Circuit Malfunction

Powertrain Fuel and Air Metering Fuel Pump Control 🟡 Moderate — Fix within a week ⚠️ Drive with Care
💬

What This Actually Means

In plain language — no jargon

The fuel pump's secondary circuit (typically a relay or driver circuit) isn't working properly, so fuel delivery is compromised. Think of it like a light switch that's broken—the pump itself might be fine, but the electrical control mechanism that turns it on is failing.

⚡

Symptoms You May Notice

3 known symptoms for this code
Engine cranks but won't start or hard starting
Loss of fuel pressure during acceleration or driving
Vehicle stalls unexpectedly while driving
🔬

How Your ECU Detects This

Technical sensor logic and voltage thresholds

The ECU monitors voltage and current draw on the fuel pump relay circuit or driver output. It expects to see proper voltage rise when the fuel pump is commanded on and detects circuit continuity with normal resistance. If voltage doesn't reach the pump or current draw is abnormal, the ECU logs a malfunction.

Voltage & Parameter Thresholds

ParameterNormal RangeFault Condition
Fuel Pump Circuit Voltage 12V when commanded on; <0.5V when off Below 10V when on or no voltage change detected
Circuit Resistance/Continuity <2 ohms relay coil resistance Open circuit or >5 ohms detected
🔧

Diagnostic & DIY Fix Guide

Check these in order — from cheapest to most complex
1
Fuel pump relay
Locate the relay in the fuse/relay box, swap it with an identical relay from another circuit to test; if fault clears, replace with new relay.
2
Fuel pump wiring harness
Inspect the pump connector and wiring for corrosion, loose pins, or broken wires; clean contacts with electrical contact cleaner and reseat connectors firmly.
3
Fuel pump ground wire
Check ground wire continuity from pump back to battery negative and clean any corroded ground connections on the frame or chassis.
⚠️

When to See a Professional Mechanic

Not all fault codes are safe to DIY

Code P1243 is a moderate fault. You can generally drive to a workshop, but avoid long trips or high-load driving (motorway, uphill towing) until it is diagnosed. If the code keeps returning after clearing, or if you notice the symptoms listed above worsening, do not delay professional diagnosis. Many moderate codes have multiple possible root causes — a mechanic with live OBD data can identify the exact fault more efficiently than part-by-part trial and error.

Safety note: OBD-II codes identify the system or circuit where a fault was detected — they do not always identify the exact failed component. A professional mechanic using live sensor data will diagnose the root cause more accurately than replacing parts based on the code alone.
🔄

How to Clear Code P1243

What happens after you fix the fault

Once the fault is repaired, P1243 can be cleared using any OBD-II scanner. Connect the scanner, navigate to "Clear Codes" or "Erase DTCs," and confirm. The check engine light turns off immediately.

The code will return if the root cause was not actually fixed. The ECM re-detects the fault within 1–3 drive cycles and sets the code again.

✅ Safe to Clear When
  • Fault has been diagnosed and repaired
  • You want to confirm the repair worked
  • Code appeared after a sensor was cleaned
⚠️ Do Not Clear When
  • Preparing for an emissions/PUC test
  • Root cause is still undiagnosed
  • Check engine light is flashing
Emissions test note: Clearing codes resets OBD readiness monitors. Most vehicles need 50–100 km of mixed driving before monitors complete. Do not clear codes immediately before an emissions or PUC inspection.