Ford Mustang 1999-2005

Exhaust Gas Recirculation (EGR) System


Description & Operation

EGR System Module

The ESM is an integrated Differential Pressure Feedback EGR (DPFE) system. It functions in the same manner as the conventional DPFE system, however the various system components have been integrated into a single component called the ESM. The flange of the valve portion of the ESM bolts directly to the intake manifold with a metal gasket that forms the measuring orifice. This arrangement increases system reliability, response time, and system precision. By relocating the EGR orifice from the exhaust to the intake side of the EGR valve, the downstream pressure signal measures Manifold Absolute Pressure (MAP). The system provides the Powertrain Control Module (PCM) with a differential DPFE signal, identical to a traditional DPFE system.

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Fig. Exhaust Gas Recirculation (EGR) System Module (ESM)

Removal & Installation

EGR System Module

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Fig. EGR system components-4.0L and 4.6L engines

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Fig. EGR system components-5.4L engine

  1. Disconnect the battery ground cable.
  3. Disconnect the Exhaust Gas Recirculation (EGR) system module vacuum tube and electrical connector.
  5. Disconnect the EGR system module to exhaust manifold tube upper fitting.
    1. To install, tighten to 29 ft. lbs. (39 Nm).
      Upon installation, make sure to install the correct EGR system module mounting gasket. Even though varying gaskets may be very similar, orifice sizes may differ thus causing performance issues.


  7. Remove the 2 bolts, the EGR system module and the gasket. Discard the gasket. To install, tighten to 18 ft. lbs. (25 Nm).
    Do not use metal scrapers, wire brushes, power abrasive disc or other abrasive means to clean the sealing surfaces. These tools cause scratches and gouges which make leak paths. Use a plastic scraping tool to remove all traces of the old gasket.

    The EGR system module sealing surfaces are soft metals.

  9. Carefully clean the EGR system module sealing surfaces.
  11. To install, reverse the removal procedure.
  13. Install a new gasket with the raised circle facing away from the EGR system module.

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    Fig. EGR ESM gasket installation



EGR System Module

EGR ESM Pin Testing

For reference values, refer to PCM testing-PCM reference voltage pin chart

This pinpoint test is intended to diagnose the following:

ESM (9Y456)
Orifice tube assembly (9D477)
Differential pressure feedback Exhaust Gas Recirculation (EGR) sensor pressure hoses
Vacuum lines
Harness circuits: VREF, DPFE, SIGRTN, EVR, VPWR and VREF

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Fig. EGR System Module pin chart