Would a bad or blocked EGR valve cause a P1400.

Here is the flow chart fore the code

CIRCUIT OPERATION

A 5-volt voltage is applied on the manifold differential pressure sensor power terminal (terminal 3) from the PCM (terminal 46). The ground terminal (terminal 2) is grounded with the PCM (terminal 57)

. - A voltage proportional to the pressure in the intake manifold plenum is sent from the manifold differential pressure sensor output terminal (terminal 1) to the PCM (terminal 91).

TECHNICAL DESCRIPTION

The manifold differential pressure sensor outputs a voltage which corresponds to the negative pressure in the intake manifold.
The PCM checks whether the voltage output by manifold differential pressure sensor is within a specified range.

DTC SET CONDITIONS

Check Conditions

Eight minutes or more have passed after starting the engine. Note that this is only if the engine coolant temperature is less than 0 °C (32 °F) when starting.
Engine coolant temperature is higher than 45 °C (113 °F).
Intake air temperature is higher than 5 °C (41 °F).
Volumetric efficiency is between 30 and 45 percent.

Judgment Criteria

Manifold differential pressure sensor output voltage has continued to be higher than 4.6 volts [corresponding to an absolute pressure of 118 kPa (17 psi) or higher] for 2 seconds. Or
Manifold differential pressure sensor output voltage has continued to be lower than 0.1 volt [corresponding to an absolute pressure of 2.4 kPa (0.3 psi) or lower] for 2 seconds.

Check Conditions

Eight minutes or more have passed after starting the engine. Note that this is only if the engine coolant temperature is 0 °C (32 °F) or more when starting.
Engine coolant temperature is higher than 45 °C (113 °F).
Intake air temperature is higher than 5 °C (41 °F).
Volumetric efficiency is lower than 30 percent.

Judgment Criteria

Manifold differential pressure sensor output voltage has continued to be higher than 4.2 volts [corresponding to an absolute pressure of 108 kPa (16 psi) or higher] for 2 seconds.

Check Conditions

Eight minutes or more have passed after starting the engine. Note that this is only if the engine coolant temperature is 0 °C (32 °F) or more when starting.
Engine coolant temperature is higher 45 °C (113 °F).
Intake air temperature is higher than 5 °C (41 °F).
Volumetric efficiency is higher than 70 percent.

Judgment Criteria

Manifold differential pressure sensor output voltage has continued to be lower than 1.8 volts [corresponding to an absolute pressure of 46 kPa (4.6 psi) or lower] for 2 seconds.

TROUBLESHOOTING HINTS (The most likely causes for this code to be set are:)

Manifold differential pressure sensor failed.
Open or shorted manifold differential pressure sensor circuit, or loose connector.
PCM failed.