Dtc P0712 Transmission Fluid Temperature (Tft) Sensor Circuit Low Input - Isuzu 1999 RODEO Workshop Manual

7A1–40 TRANSMISSION CONTROL SYSTEM (4L30–E)

DTC P0712 Transmission Fluid Temperature (TFT) Sensor Circuit Low Input

Circuit Description
The TFT sensor is a thermister that controls the signal
voltage to the PCM. The PCM supplies a 5–volt reference
signal to the sensor on circuit GRN/RED. When the
transmission fluid is cold, the sensor resistance is high.
The PCM detects high signal voltage.
transmission fluid temperature increases to the normal
operating temperature of 100°C (212°F), the sensor
resistance becomes less and the voltage decreases to
1.5 to 2 volts. With transmission fluid over temperature
and DTC P0218 also set, check the transmission cooling
system.
This DTC detects a continuous short to ground in the TFT
signal circuit or the TFT sensor. This is a type "D" DTC.
Conditions For Setting The DTC
f Battery voltage is between 10 and 16 volts.
f Ignition is "on".
f TFT sensor indicating a voltage less than 0.4 volts.
f All conditions met for 20 seconds.
Action Taken When The DTC Sets
f Transmission default temperature will be:
80°C (176°F) if engine temperature code is set.
100°C (212°F) if engine temperature is warm.
80°C (176°F) if engine run time is greater than 5
minutes.
21°C (69.8°F) if engine run time is less than 5
minutes.
f The PCM will not illuminate the Malfunction Indicator
Lamp (MIL).
Conditions For Clearing The DTC
f The DTC can be cleared from the PCM history by
using a scan tool.
f The DTC will be cleared from history when the vehicle
has achieved 40 warmup cycles without a failure
As the
reported.
f The PCM will cancel the DTC default actions when
the fault no longer exists and the ignition is cycled "off"
long enough to power down the PCM.
Diagnostic Aids
f Check harness routing for a potential short to ground
in circuit GRN/RED. Scan tool TFT display should
rise steadily to about 100°C (212°F), then stabilize.
f Inspect the wiring for poor electrical connection at the
PCM and at the transmission 16–way connector.
Look for possible bent, backed out, deformed or
damaged terminals. Check for weak terminal tension
as well. Also check for a chafed wire that could short
to bare metal or other wiring. Inspect for a broken wire
inside the insulation.
f When diagnosing for a possible intermittent short or
open condition, move the wiring harness while
observing test equipment for a change.
f The temperature to resistance value scale may be
used to test the TFT sensor at the various
temperature levels to evaluate the possibility of a
"skewed" (mis–scaled) sensor.
A "skewed" sensor could result in delayed garage
shifts or TCC complaints.
f Verify customer driving habits, trailer towing, etc.
D07RW018