Usage:
3406B ( 2EK ) PEEC and 3176 ( 7LG ) Diesel Engines
Reference: 3176 Diesel Truck Engine:Electronic Troubleshooting, SENR5112
Reference: 3176 Diesel Truck Engine:Systems Operation, Testing & Adjusting, SENR5108.
Reference: 3406B PEEC Diesel Truck Engine:Electronic Troubleshooting, SENR3479-04 (or later issue)
Reference: 3406B PEEC Diesel Truck Engine:Systems Operation, Testing & Adjusting, SENR3485-02 (or later issue).
A new diagnostic code is being included on 1991 Engines. The new Code 28 is, "Check Throttle Sensor Adjustment".
The new diagnostic Code 28 is intended to indicate when the Throttle Position Sensor (TPS) is severely misadjusted. Code 28 becomes active when pulse width falls below 5% or rises above 95%. The check engine lamp will come on to warn the driver that service is required, and the code will be logged in permanent memory.
Note that Code 28 only indicates when the TPS is severely misadjusted. The absence of an active Code 28 is not by itself an accurate indicator that the linkage on the remote mounted Throttle Position Sensor is adjusted correctly.
The Remote Mounted Throttle Position Sensor must be adjusted. When correctly adjusted, the remote mounted TPS will produce a pulse width (duty cycle) signal of 15% to 20% at the low idle stop, and 80% to 85% at the high idle stop.
The Pedal Mounted TPS is not adjustable. It will produce a pulse width signal just like the Remote Mounted sensor. The acceptable range of the Pedal Mounted sensor is from 10% to 22% at the low idle stop, and 75% to 90% at the high idle stop. Since the stops on these pedals are controlled by pedal dimensions and are not adjustable, an active Code 28 with this sensor will most likely indicate a problem with the pedal rather than the sensor.
On engines equipped with the new Personality Module, new Service Program Modules (SPM) for the ECAP allow "Throttle Duty Cycle" to be read directly from the ECM, without using the Pulse Width Modulation Probe. This saves time, and makes it easier to read the sensor pulse width signal. Select "Calibrate/Monitor Sensors" from the ECAP menu screens to display the duty cycle as seen by the ECM. Previous versions of SPM or Personality Modules must still use the probe.
For the correct method of adjusting the Throttle Position Sensor, refer to the appropriate reference.