74 Calculated Oil Temperature In Use

Test 74 - Calculated Oil Temperature In Use (96 My and Later Only)






THEORY OF OPERATION:
In all 1996 model year vehicles except for early NS vehicles (without TRS) the TCM uses a thermistor to monitor the transmission's sump temperature. This temperature is used to determine which shift schedule the TCM is to use. If the thermistor circuit fails to operate properly the TCM will use the calculated oil temperature routine found in prior model year TCM's. If this occurs for three consecutive key starts, the code will be set. The TCM will then test the thermistor circuit after every 35 OBDII warm-up starts. If the thermistor circuit is OK, the thermistor data is used in place of the Calculated Oil Temperature Routine.

LIMP-IN:
NO

WHEN MONITORED/SET CONDITIONS:
Whenever the engine is running.

The code is set if any of the following conditions exist for three consecutive key starts:
- The thermistor voltage is out of range (below 0.07 volts or greater than 4.94 volts)
- If continuous erratic thermistor voltage is sensed.
- The thermistor temperature stays below 80° F for an extended period of time.

TRANSMISSION EFFECTS:
96 model year - Prior to setting this code, the transmission may operate in the wrong shift schedule for the existing conditions. After the code is set, the transmission will use a "calculated oil temperature" and normal operation will resume. After 35 OBDII warm-up starts, the TCM will attempt to use the thermistor circuit. If the problem is still present, the wrong shift schedule may be selected until the code is set again.

97 MY and later - If the thermistor indicates a temperature below 0° F at start up, the TCM compares the calculated oil temperature to the indicated thermistor oil temperature. If the calculated oil temperature differs significantly from the thermistor value, the calculated oil temperature will be used for that key start.

POSSIBLE CAUSES:
- Wiring or connector problems in the transmission temperature sensor signal circuit,
- Defective TRS
- Defective TCM

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