What Does P1242 Mean?
DTC P1242 indicates a malfunction in the fuel pump secondary circuit, typically representing a different fault condition or threshold from P1238. The FPDM or PCM has detected irregular electrical behavior on the secondary circuit that delivers power to the fuel pump, which could involve voltage spikes, dropouts, or out-of-range current readings during operation.
Common Causes
30%
Fuel pump motor with degraded brushes causing electrical noise
25%
Intermittent connection in fuel pump secondary wiring
20%
FPDM secondary circuit driver degradation
15%
Fuel pump connector with intermittent contact due to vibration
10%
Fuel pump drawing excessive current due to clogged fuel filter or strainer
Diagnostic Steps
1
Monitor fuel pump current draw with a clamp-on ammeter while the engine is running at various loads — look for erratic spikes or drops in current.
2
Inspect the fuel pump strainer/filter for clogging that could increase pump workload and cause secondary circuit stress.
3
Wiggle-test the fuel pump harness connector at the tank while monitoring fuel pressure and pump operation for intermittent connections.
4
Check the FPDM for any stored diagnostic information or self-test capability using a manufacturer-specific scan tool.
5
Measure secondary circuit voltage at the fuel pump connector during steady-state operation and compare to FPDM output voltage — significant difference indicates wiring resistance.
Estimated Repair Cost
$150 - $700
Parts + labor, varies by vehicle and location
DTC P1242 indicates a malfunction in the fuel pump secondary circuit, typically representing a different fault condition or threshold from P1238. The FPDM or PCM has detected irregular electrical behavior on the secondary circuit that delivers power to the fuel pump, which could involve voltage spik...
The most common cause of P1242 (Fuel Pump Secondary Circuit Malfunction) is: Fuel pump motor with degraded brushes causing electrical noise
Typical repair costs for P1242 range from $150 to $700, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Secondary circuit malfunctions can cause intermittent fuel pressure drops, resulting in hesitation or stumbling during acceleration. While not immediately dangerous at low speeds, these symptoms can be hazardous during highway driving.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P1242 to identify the root cause.
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Quick Info
Category
Powertrain
System
Fuel Delivery
Difficulty
Type
Manufacturer
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