Auxiliary Throttle Valve System Malfunction (Nissan)
What does P1503 mean?
The P1503 code means the vehicle's onboard diagnostic system has detected: Auxiliary Throttle Valve System Malfunction (Nissan). This is a moderate severity code.
Common Symptoms
- Reduced engine power or limp mode
- Check Engine Light illuminated
- Throttle response is slow or unresponsive
- Engine idle may surge or fluctuate
- Vehicle may not accelerate past a certain speed
Probable Causes (Ranked by Likelihood)
- Faulty electronic throttle body Very High
- Throttle position sensor failure High
- Carbon buildup restricting throttle plate movement High
- Damaged wiring to the throttle body Moderate
- Faulty accelerator pedal position sensor Low
Step-by-Step Diagnostic Procedure
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Use a scan tool to monitor throttle position and accelerator pedal position while moving the pedal slowly.
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Clean the throttle body with throttle body cleaner. Carbon buildup is a very common cause on Nissan engines.
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Inspect the throttle body connector for corrosion, bent pins, or water intrusion.
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Check the throttle body motor by commanding it with a scan tool and observing plate movement.
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Test the accelerator pedal position sensor for smooth, linear output across its full range.
Frequently Asked Questions
Why does my Nissan go into limp mode?
When the ECU detects a throttle system malfunction, it limits engine power to a safe level as a protective measure. This prevents unintended acceleration or other unsafe conditions.
Can cleaning the throttle body fix this?
In many cases, yes. Carbon buildup on the throttle plate and bore is a leading cause of throttle system codes on Nissan vehicles. Cleaning is a low-cost first step before replacing parts.
Do I need to relearn the throttle after cleaning?
Yes. After cleaning or replacing the throttle body on most Nissan vehicles, you must perform an idle air volume learning procedure. This can be done with a scan tool or through a specific key-on sequence.