P0668

PCM/ECM/TCM Internal Temperature Sensor Circuit Low

P0668 is a generic OBD-II powertrain diagnostic trouble code: PCM/ECM/TCM Internal Temperature Sensor Circuit Low. It is logged by the engine control unit when the powertrain monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.

Code
P0668
Group
Powertrain
System
Powertrain
Severity
Warning (MIL on)
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What P0668 means

P0668 is set when the control module detects that its internal temperature sensor circuit voltage is below the minimum expected threshold. The internal sensor monitors the module's own temperature to protect its electronics, and the module watches the resulting signal against calibrated low and high limits.

A signal below the low limit indicates a short to ground in the sensor circuit, a failed sensor element, a power supply or ground problem, or an internal module hardware fault. Although the sensor element sits inside the module, the associated reference and ground circuits, connector pins, and module power feed are all fair game for inspection. This code is frequently misdiagnosed as an actual engine or transmission overheating problem when it is really an electrical fault within the sensing circuit.

Severity varies widely. Many vehicles run normally with only the lamp illuminated, but sources note the engine may stall, fail to start, or run with sputtering or power loss when the fault is active. Because of that variability, and because unnecessary module replacement is common, technicians should confirm power, grounds, and connections before condemning the module.

Common causes

Most-frequently reported root causes when P0668 is logged.

  • 1
    Short to ground in the internal temperature sensor circuit.
  • 2
    Failed internal temperature sensing element reading low.
  • 3
    Poor module power supply or ground affecting the reference voltage.
  • 4
    Corroded, damaged, or loose module connector pins.
  • 5
    Moisture or contamination inside the module causing circuit shorting.
  • 6
    Damaged wiring near the module affecting the sensor circuit.
  • 7
    Module hardware fault collapsing the internal sensor reference.
  • 8
    Corrupted module software misinterpreting the low signal.

Symptoms drivers notice

Check engine light or transmission warning lamp illuminated.
Often no immediate drivability impact in mild cases.
Possible engine stalling or failure to start.
Sputtering or power loss if the engine keeps running.
Companion internal module codes may be stored.

How to diagnose P0668

A typical diagnostic flow when this code is present.

  1. 1
    Connect a scan tool and record all DTCs, noting any other internal module codes.
  2. 2
    Perform a visual inspection of the module wiring, ground straps, and harness for chafing or damage.
  3. 3
    Inspect the module connector for corrosion, moisture, and bent or backed-out pins.
  4. 4
    Verify module power supply and ground voltages meet specification.
  5. 5
    Observe the internal temperature value in live data if supported and compare to ambient conditions.
  6. 6
    Apply a module software update if a relevant calibration is available.
  7. 7
    If wiring and power are good but the fault persists, evaluate the module for internal failure.

Related powertrain codes

Frequently asked questions

Is P0668 different from P0667?

Yes. P0667 is a range or performance fault, while P0668 specifically means the internal temperature sensor circuit voltage is below the minimum expected level.

Is there any wiring to check for P0668?

Yes. Although the sensor element is inside the module, the module power feed, grounds, and connector pins can all cause a low signal, so inspect them first.

Can P0668 stop the car from running?

It can. Depending on the vehicle, the engine may stall, fail to start, or run with sputtering and power loss when the fault is active.

Could a programming error cause P0668?

Yes. Corrupted or incorrect calibration data can cause the module to misinterpret its internal sensor signal and set this low-circuit code.

Disabling P0668 in software

RaceTune can permanently disable P0668 — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.

Permanent
The monitor is disabled in the ECU itself — not just cleared. It cannot return.
Tailored to your file
Each patch is matched to your specific software version — never a one-size-fits-all file.
Reversible
The original file is always preserved. Reflash the stock to return the ECU to factory state.

ECU families we can disable P0668 on

We hold the DaVinci A2L disable definitions for these families, so the exact P0668 path and mask addresses are mapped. verified marks a confirmed disable definition. We support many more — upload your file and our identifier will match it automatically.

  • Bosch EDC17C66 verified
  • Bosch EDC17CP57 verified

Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.

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