In Toyota, the P1603 code is a DTC showing engine stall due to lower common rail fuel pressure. It could be any number of issues from a simple low on fuel issue, to major mechanical failures.
P1603 Code Common Causes
Low or Contaminated Fuel
This code can also result from an empty or near empty fuel tank.
Bad-quality or mixed-up fuel can clog the fuel system and affect efficiency.
Fuel System Issues
When the fuel filter gets clogged or dirty they fould less flow of fuel causing pressure drops.
The delivery of the fuel can degrade by faulty fuel injectors or wrong compensation codes.
An insufficient fuel pressure can be caused by a failed fuel pump or common rail assembly.
Electric and Sensor Failures
Random engine stalls can come from weak or failing batteries.
Examples of failing sensors include the coolant temperature sensor, which transmits inaccurate information to the engine control unit (ECU), resulting in erroneous fuel injection timing.
An ECU failure that misreads fuel pressure data could also set this code, though that’s quite rare.
Mechanical Problems
The less frequent is due to low cylinder compression, which may cause engine stalls.
In fairness, the cleanliness of the engine may support that claim, but malfunctioning glow plugs can lead to cold starting difficulties, rough running and use the fuel in minutes.
Symptoms of the P1603 Code
Loss of engine power, particularly during load or at idle.
Hard time restarting the engine after a stall
Idling rough or hesitation during acceleration.
Dashboard warning lights, such as the check engine light.
Diagnosing and Repairing the P1603 Code
Step 1: Check the Basics
Make sure the vehicle has an ample supply of fuel.
Check if the battery is healthy, and the voltage, to eliminate electrical problems.
Step 2: Check for Fuel Supply
Look for fuel contamination: review recent fueling history.
Check and replace clogged fuel filter.
Check all 8 fuel injectors — especially the compensation codes — to ensure everything is properly calibrated.
Step 3: Inspect Internal Mechanicals
If weak cylinder compression is suspected, perform a compression test.
Check functionality of the glow plugs and the coolant temperature sensor.
Stage 4: Investigate the Fuel Pressure and Delivery System
Verify where seals or obstructions may be located in the fuel pump and simpler common rail setup.
Scan the ECU for more error codes and reset if needed.
How can you fix P1603?
On the assumption that the problem lies with a blocked fuel filter, replacing it will reinstate fuel flow and clear the P1603 code. If that’s the case and the problem still occurs, you may need to diagnose the fuel pump, sensors, or ECU.
Using these diagnostic steps, Toyota owners can provide a thorough diagnosis to the P1603 and avoid stalling their engine.