P1242

Fuel Pump Secondary Circuit Malfunction

Powertrain Fuel and Air Metering Fuel pump circuit 🟡 Moderate — Fix within a week ⚠️ Drive with Care
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What This Actually Means

In plain language — no jargon

Your vehicle's backup fuel pump isn't working properly, like having a second water pump that can't kick in when needed. The engine computer detected a wiring or component problem in the secondary fuel pump circuit.

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Symptoms You May Notice

3 known symptoms for this code
Engine stalls or hesitates during acceleration
Difficulty starting, especially after sitting overnight
Fuel pump relay clicking heard but engine won't turn over
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How Your ECU Detects This

Technical sensor logic and voltage thresholds

The ECM monitors voltage and current draw from the secondary fuel pump circuit, typically when the primary pump fails or during high-demand conditions. It detects open circuits, short circuits, or excessive resistance in the wiring harness and pump motor. The fault triggers when voltage or current falls outside safe operating parameters.

Voltage & Parameter Thresholds

ParameterNormal RangeFault Condition
Secondary pump circuit voltage 10.5-14.5V under load Below 9V or open circuit detected
Pump motor current draw 4-8 amps steady state Zero amps or above 10 amps
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Diagnostic & DIY Fix Guide

Check these in order — from cheapest to most complex
1
Secondary fuel pump relay
Locate the relay in the engine bay fuse box and swap it with an identical relay from another circuit to test continuity.
2
Fuel pump wiring harness connector
Inspect the connector for corrosion, loose pins, or water intrusion and clean with electrical contact cleaner.
3
Secondary fuel pump assembly
If wiring and relay test good, replace the secondary pump in the fuel tank after depressurizing the fuel system.
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When to See a Professional Mechanic

Not all fault codes are safe to DIY

Code P1242 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.
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How to Clear Code P1242

What happens after you fix the fault

Once the fault is repaired, P1242 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.