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Exhaust Gas Recirculation Cooler Bypass Control Circuit

The Exhaust Gas Recirculation (EGR) Cooler bypass valve is used to bypass the EGR cooler when the engine is in an active regeneration mode. This is to prevent EGR cooler fouling. There are two portions to this diagnostic. At key on the Engine Control Module (ECM) drives the control line low and then high and monitors the correct status response. Throughout engine operation looks for status response voltage to be within 5-8 volts. The EGR Cooler Bypass valve will send a signal between 1.0 and 1.7 volts. When this occurs the ECM logs a fault. The second portion of this diagnostic monitors Exhaust Gas Recirculation temperature. If the EGR Cooler Bypass valve was in bypass mode incorrectly, the exhaust gas recirculation temperatures would exceed a temperature limit; this condition will also trigger the fault. The ECM will light a MIL lamp immediately after this diagnostic runs and fails. The ECM will turn off the MIL lamp after the diagnostic passes in four consecutive drive cycles.

Cause:
Coolant System
EGR Cooler
Faulty Exhaust Gas Recirculation (EGR) Temperature Sensor
Exhaust Gas Recirculation (EGR) Temperature Sensor harness is open or shorted
Exhaust Gas Recirculation (EGR) Temperature Sensor circuit poor electrical connection

Symptoms:
Check engine light