PINPOINT TEST DL: Cylinder Head Temperature (CHT) Sensor: Introduction
Do not disconnect, disable, or touch the high voltage cables, components, or wiring during the module reprogramming procedure because high voltage is present. The high voltage warning labels containing the high voltage symbol are located on each high voltage component. High voltage cables and wiring are orange in color. Failure to follow these instructions may result in personal injury or death.
Appropriate repair methods and procedures are essential for the safe, reliable operation of all motor vehicles, as well as the personal safety of the individual doing the work. This article provides general directions for repairing vehicles with tested, effective techniques. Following them helps to establish reliability. There are numerous variations in procedures, techniques, tools, and parts for repairing vehicles, as well as in the skill of the individual doing the work. This article cannot possibly anticipate all such variations and provide advice or cautions as to each. Accordingly, anyone who departs from the instructions provided in this article must first establish that they compromise neither their personal safety nor the vehicle integrity by their choice of methods, tools, or parts.
This pinpoint test is intended to diagnose the following:
- cylinder head temperature (CHT) sensor (6G004)
- harness circuits: CHT, VREF, and SIGRTN
- powertrain control module (PCM) (12A650)
On applications that do not use an ECT sensor, the CHT sensor is used to determine the engine coolant temperature in place of the ECT sensor. To cover the entire temperature range of both the CHT and ECT sensors, the PCM has a dual switching resistor circuit on the CHT input. A graph showing the temperature switching from the COLD END line to the HOT END line, with increasing temperature and back with decreasing temperature is included. Note the temperature to voltage overlap zone. Within this zone it is possible to have either a COLD END or HOT END voltage at the same temperature. For example, at 90°C (194°F) the voltage could read either 0.60 volt or 3.71 volts. Refer to the table for the temperature to voltage expected values.
Voltage values calculated for VREF = 5 volts. These values can vary by 15% due to sensor and VREF variations.
| temperature | CHT Sensor Values | |||
|---|---|---|---|---|
| °C | °F | COLD END (volts) | HOT END (volts) | Resistance (K ohms) |
| -40 | -40 | 4.89 | - | 965.808 |
| -30 | -22 | 4.81 | - | 513.019 |
| -20 | -4 | 4.67 | - | 283.664 |
| -10 | 14 | 4.45 | - | 162.584 |
| 0 | 32 | 4.14 | - | 96.255 |
| 10 | 50 | 3.73 | - | 59.175 |
| 20 | 68 | 3.26 | - | 37.387 |
| 30 | 86 | 2.74 | - | 24.215 |
| 40 | 104 | 2.23 | - | 16.043 |
| 50 | 122 | 1.76 | - | 10.85 |
| 60 | 140 | 1.36 | - | 7.487 |
| 70 | 158 | 1.04 | - | 5.268 |
| 80 | 176 | 0.79 | 3.99 | 3.775 |
| 85 | 185 | 0.69 | 3.86 | 3.215 |
| 90 | 194 | 0.60 | 3.71 | 2.75 |
| 95 | 203 | 0.53 | 3.56 | 2.361 |
| 100 | 212 | 0.46 | 3.41 | 2.034 |
| 110 | 230 | - | 3.07 | 1.523 |
| 120 | 248 | - | 2.74 | 1.155 |
| 130 | 266 | - | 2.41 | 0.8866 |
| 140 | 284 | - | 2.10 | 0.6891 |
| 150 | 302 | - | 1.81 | 0.5417 |
| 160 | 320 | - | 1.55 | 0.4301 |
| 170 | 338 | - | 1.33 | 0.3449 |
| 180 | 356 | - | 1.13 | 0.2791 |
| 190 | 374 | - | 0.96 | 0.2278 |
| 200 | 392 | - | 0.82 | 0.1875 |
| 210 | 410 | - | 0.70 | 0.155 |
| 220 | 428 | - | 0.60 | 0.130 |
| 230 | 446 | - | 0.51 | 0.109 |
| 240 | 464 | - | 0.44 | 0.092 |
| 250 | 482 | 0.35 | 0.078 | |
| 260 | 500 | 0.33 | 0.067 | |
| Pin | Circuit |
|---|---|
| 2 | SIGRTN (Signal Return) |
| 1 | CHT (Cylinder Head Temperature) |
| Pin | Circuit |
|---|---|
| E40 | VREF (Reference Voltage) |
| E41 | SIGRTN (Signal Return) |
| E33 | CHT (Cylinder Head Temperature) |