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Error Code P1408 is described as EGR (Exhaust Gas Recirculation) out of self-test range. This means the EGR valves are not functioning properly, causing it to send readings that are outside the set range.
This error code is a manufacturer-specific trouble code, meaning it does not apply to all vehicles makes. Rather, it applies only to specific vehicle makes, such as Ford. Specification on the definition, troubleshooting, and repairs still vary from one make and model to another.
The job of the EGR system is to reduce combustion temperatures and exhaust gas NOx (Nitrogen Oxide) content by recirculating a portion of the exhaust gas into the intake manifold under normal vehicle driving conditions. The amount of exhaust gas recirculated varies from 0 with a cold engine to a fixed rate for a hot engine with an intermediate load and low engine speed.
To test this, a KOER (Key On Engine Running) test must be made. The EGR system is commanded On at a fixed engine speed. The vehicle will fail the test when the DTC (Diagnostic Trouble Code) is output when the measured EGR flow falls above or below the calibration requirements set by the manufacturer for the vehicle.
As with other error codes, P1408 activates the Check Engine light and registers the code to the vehicle’s system. For some vehicles models such as Ford Focus, the vehicle may exhibit drivability issues, such as misfiring and hesitation.
Error Code P1408 can be caused by a couple of things, such as:
- Defective EGR valve
- Defective or off EGR valve vacuum hose
- Plugged EGR valve
How to Check
This fault code also means EGR valve circuit failure. Thus, to start your diagnosis, you can check the EGR valve first; look for signs of dirt to clean the port.
Check the downstream passage connected from the port to the throttle body.
For some engine models, you may have to check the Upper Intake Manifold.
How to Fix
Repairs for this code are as easy as its diagnosis. But of course, you need to conduct a thorough diagnosis before you can start any repairs.
Start with the EGR valve; remove and clean the EGR valve pintle rod, and at the same time, clean the opening of the EGR port where the valve is mounted.
If you can, clean the passage that goes downstream from the port up to the throttle body. Use the air blower to blow the passage and soak it with carb cleaner spray to remove carbon buildup which is what usually restricts the exhaust gas passage.
For some engine models, to access the port openings, you may have to remove the upper intake manifold. It’s a simple process by nature, but it can be quite extensive.
Also, for many engine models, EGR valve cleaning is the obvious route when this fault code comes out. However, if the vehicle has lots of mileage, it is better to replace the EGR valve completely. This is because cleaning the valve may take a lot of time, and failure is still a possibility. This is especially true if you have removed the intake manifold already, and the cost to replace the EGR valve is not too expensive as cleaning the valve when you buy a brand new.
For owners of newer Ford engines, it is required to replace the DPFE (Delta Pressure Feedback) sensor before replacing the EGR valve. This component monitors the differential vacuum pressure to measure the exhaust gas that flows to the EGR valve. The difference in the vacuum is that it is sent as a signal to the ECM to control the EGR valve’s openings.
For some EGR Ford Focus systems, the DPFE system is known to fail if the engine shows misfire or hesitation symptoms. To verify the DPFE sensor, check the solenoid wirings that is attached to it and measure the supply and ground voltage. Again, if you’re deciding to replace the DPFE sensor or the EGR Ford Focus valve, you should replace the latter first for maintenance of the engine, especially if it shows up as an Error Code P1408. However, you should remember that cleaning the EGR valve is also one way to verify if the code is serious or permanent.
Error Code P1408 is a common problem among 2.5, 3.0 Duratec and 4.6 liter engines.