CM850 Electronic Control System – FAULT CODE 9121

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Overview

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Circuit Description

The electronic control module (ECM) controls the exhaust gas recirculation
(EGR) valve, opening and closing it based on various engine operating conditions. The EGR valve is opened and closed by a VDC motor that receives voltage from the ECM on the EGR valve motor signal (+) and EGR valve motor signal (-) circuits. To open the valve, the motor receives voltage on the EGR valve motor signal
(+) circuit. To close the valve, the motor receives voltage on the EGR valve motor signal (-) circuit.

Component Location

The EGR vale motor is located on the exhaust side of the engine and is attached to the EGR valve assembly, which is mounted to the exhaust manifold. Refer to Procedure 100-002 for a detailed component view.

Shop Talk

The ECM calculates the temperature of the EGR valve motor. If the ECM detects excessive temperatures for a calibrated period of time this fault is recorded and the valve is commanded closed. This action is for protection of the valve only; this fault code is not indicative of any component failure. Once the ECM detects normal EGR valve temperatures, the fault code will go inactive and the EGR valve operation will resume.

NOTE: During this event, there will be no noticeable symptoms. This troubleshooting tree should not be considered if there is a performance complaint.

A combination of frequent valve movement and elevated coolant temperatures can lead to this fault code.

Refer to Troubleshooting Fault Code t05-9121