P0713 and P0712 Transmission Fluid Temperature Sensor: Diagnosis, Causes, and the Real Fix

P0713 and P0712 Transmission Fluid Temperature Sensor: Diagnosis, Causes, and the Real Fix

P0713 and P0712 Transmission Fluid Temperature Sensor: Diagnosis, Causes, and the Real Fix

You plug in a scan tool and the transmission fluid temperature reads -40°F on a truck that has been idling for twenty minutes. Or it reads 300°F on a cold start in January. Either way the shifts got firm, the torque converter clutch quit locking, and a P0713 or P0712 is stored. The sensor itself is almost never sold as a stand-alone piece — and that is exactly why this code sends so many people down the wrong repair path.

4L80E Transmission Range Sensor (MLPS) 1991-2013 OEM 24229422
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4L80E Transmission Range Sensor (MLPS) 1991-2013 OEM 24229422
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What the two codes actually mean

The transmission fluid temperature (TFT) sensor is a negative temperature coefficient thermistor: resistance falls as the fluid heats up. Per OBD-Codes, the TFT sensor signal voltage goes down when fluid temperature goes up, and P0713 sets when the controller sees a high signal — which usually means an open circuit.

  • P0713 — Circuit High Input. Open wire, open sensor, or a lost ground. The module reads the coldest value in its table, typically -40°F.
  • P0712 — Circuit Low Input. The mirror image: a short to ground, so the module reads an impossibly hot value.

On the GM 4L80E, the pre-OBD-II versions of these are DTC 59 (circuit high, low temperature indicated) and DTC 58 (circuit low). The AM General 4L80E troubleshooting supplement spells out the circuit: "The TCM supplies a 5 volt reference signal to the sensor on CKT 923. When the transmission fluid is cold, the sensor resistance is high and the TCM will sense high signal voltage." It also gives the set criteria — signal voltage indicating below -40°C, held for one second — and notes the module then uses "a warm default trans fluid temperature value" (4L80E Transmission Troubleshooting, p.80).

That default value is why the truck still drives. It is also why shift quality goes sideways: the controller is guessing at fluid temperature while it sets line pressure, shift timing, and converter lockup.

Where the sensor actually lives

This is the part most write-ups skip. On the great majority of units the TFT sensor is not a screw-in part. As CarParts.com puts it, it is "either part of the solenoid pack or the valve body harness rather than being serviced separately."

GM is specific about it. ATRA Technical Bulletin #269 maps the 4L60E case connector and lists the "Transmission Fluid Temperature Sensor (located in PSA)" on pins L and M — PSA being the pressure switch assembly, the manifold bolted to the valve body (ATRA TB #269). On the 4L80E the thermistor is molded into the internal wiring harness instead. Same code, two completely different parts.

Diagnosis: five steps, pan still on

  1. Read the live data cold. Key on, engine off, on a vehicle that has sat overnight. TFT should track close to ambient. A hard -40°F or a pegged-hot value confirms the circuit, not the fluid.
  2. Ohm the sensor at the case connector. Unplug the external connector and measure across the two TFT pins — L and M on a 4L60E per ATRA TB #269. Compare to the chart below.
  3. Simulate the opposite fault. The 4L80E procedure for DTC 59 has you install a test light between terminals L and M with the ignition on; the scan tool "should display temperature of 151°C (306°F)." If it does, the module and external wiring are good and the fault is inside the case.
  4. Check the reference and the return. Same source: "A faulty connection or an open in CKT 359 or CKT 923 can result in a DTC 59." Confirm 5 volts at the sensor connector and continuity on the ground leg before condemning anything internal.
  5. Watch it sweep. With the meter still on the pins, idle the engine in gear. A healthy thermistor drops steadily in resistance as the unit warms.

TFT resistance reference

Nominal values from ATRA TB #269 (4L60E, pins L and M): 100,544 ohms at -40°F, 9,379 ohms at 32°F, 3,520 ohms at 68°F, 333 ohms at 176°F, and 154 ohms at 213°F.

The 4L80E supplement publishes a tolerance band rather than a single figure. Its Table 21 lists 2,981 / 3,500 / 4,018 ohms (minimum / nominal / maximum) at 69°F and 158.1 / 177.4 / 196.8 ohms at 212°F. The quick field chart in Table 22 is easier to use with a hot pan: roughly 7,500 ohms at 40°F, 3,400 at 70°F, 1,800 at 100°F, 450 at 160°F and 185 at 210°F.

Read those numbers carefully, because the same document warns that the chart may be used "to evaluate the possibility of a 'skewed' (mis-scaled) sensor," and that "a 'skewed' sensor can result in firm shifts, or TCC complaints." A skewed sensor reads plausibly but wrongly and sets no code at all — it is the version of this failure that gets misdiagnosed as a worn clutch pack.

The fix: which part, and why

Once the in-case test points to the sensor, the repair is decided by which unit you are in.

4L60E manifold pressure switch OEM 24215111, the assembly that houses the transmission fluid temperature sensor
On the 4L60E the TFT thermistor lives inside the pressure switch manifold, so the manifold is the service part.

The rest of the electrical hardware for both units is grouped in the transmission sensors collection, and shift, EPC and TCC solenoids are in solenoids.

Replace while you are in there

You are dropping the pan and pulling the filter regardless. Do these at the same time:

  • Filter and pan gasket — never reuse either.
  • Case connector O-ring or seal, whether or not you replace the connector itself.
  • Manifold and harness connector locks, if the plastic has gone brittle from heat.
  • TCC and shift solenoid screens if the fluid shows debris.
  • Fresh fluid to the correct spec. The 4L80E supplement calls for Dexron III in that application and says to check level only at normal operating temperature, "180-200°F (82-93°C)," reached after roughly 15 miles of driving. Use the fluid your specific model year calls for.

Cost and effort

This is a low-difficulty job by transmission standards. A case connector pigtail is a 30 to 45 minute repair with the vehicle on ramps. A pressure switch manifold or an internal harness is a pan-down job: budget 1.5 to 2.5 hours in a two-wheel-drive car, more in a four-wheel-drive truck where the crossmember or transfer case linkage is in the way. Both parts sit right at the valve body, so no unit removal and no teardown are required. Compared with the alternative — a rebuild recommended off a misread temperature value — it is the cheapest fault in the electrical section of these transmissions to fix correctly.

FAQ

Can I just clear P0713 and drive it? Mechanically the unit will move, because the controller substitutes a default warm fluid temperature. But it is then setting line pressure and lockup off a guess, and that is how clutches get cooked over a few thousand miles.

Why does my scan tool read exactly -40°F? That is the bottom of the lookup table, not a measurement. An open circuit drives signal voltage to the reference value, and the module reports the coldest temperature it knows. -40 is also the point where Fahrenheit and Celsius meet, so it looks the same on either scale.

Can the TFT sensor be bad without setting a code? Yes, and it is the case worth knowing about. A skewed thermistor reads inside the legal voltage window but off the real curve. The 4L80E service literature ties that condition directly to firm shifts and torque converter clutch complaints. Ohm it against the chart at a known temperature instead of trusting the code list.

Related reading: P0218 transmission fluid over temperature and the 6L80 pressure switch manifold and phantom shifts.

Sources