CAT Engine 2634 Fault Code: Digital Sensor Supply short to ground
Also called Digital Sensor Power Supply (8V Or 12V) : Voltage Below Normal, Digital Sensor Power Supply (8V Or 12V) Voltage Below Normal, Digital Sensor Power Supply (8V Or 12V) voltage below normal, Digital Sensor Power Supply (8V Or 12V): Voltage Below Normal, Digital Sensor Supply Short to Ground
Digital Sensor Supply short to ground · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
Code 2634 (SPN 678 / FMI 4) means the ECM has detected that the digital sensor supply voltage has dropped below normal, indicating a short to ground. This affects digital sensors like the throttle position sensor, coolant level sensor, exhaust temperature sensors, or decelerator position sensor depending on the engine model. When active, the ECM forces all digital sensor readings to default values, which can cause low power or other operating problems.
High severity. This code is not an immediate stop-engine emergency, but because the ECM substitutes default values for all digital sensors while the fault is active, the engine can lose accurate control input and may run in a low-power or degraded mode. Diagnose promptly to avoid extended operation on default sensor data.
What does CAT Engine error code 2634 mean?
Code 2634 relates to the digital sensor power supply circuit inside the CAT ECM, which powers the digital-style sensors on the engine. Depending on the specific engine and configuration, this circuit can supply either 12.7 volts (plus or minus 1.0 volts) or 8.0 volts (plus or minus 0.4 volts) to sensors such as the throttle position sensor, coolant level sensor, auxiliary temperature sensor, left and right exhaust temperature sensors, and the decelerator position sensor.
The ECM feeds this regulated voltage out to pin A on each digital sensor connector, with the sensor return going back to the ECM on pin B. This supply is short-circuit protected against a short to battery positive or battery negative, so a short will not damage the internal ECM circuitry. However, the sensors themselves are not protected from overvoltage, so a short from the supply line to battery positive can damage a connected sensor.
When the ECM sees the supply voltage sag below the threshold for the specified time, it concludes there is a short to ground somewhere on that supply circuit. It logs the code and forces every digital sensor to a default value, regardless of what the sensors are actually reading at that moment. This can mask real sensor data and may cause the engine to run in reduced power.
What triggers a CAT Engine 2634 code?
For the 12-volt supply system, the ECM sets this code when it reads a digital sensor supply voltage below 11.7 volts for at least 2 seconds, and only after the ECM has been powered up for at least 3 seconds. Normal voltage on this circuit is 12.7 volts plus or minus 1.0 volts. For the 8-volt supply system used on some engines, the ECM sets the code when it reads a digital sensor supply voltage below 7.5 volts for 2 seconds, again after the ECM has been powered for 3 seconds. Normal voltage on that circuit is 8.0 volts plus or minus 0.4 volts.
Common causes of 2634
- Damaged or corroded connectors, or damaged wiring, anywhere in the digital sensor supply circuit
- A problem within the wiring harness itself, such as a pinched or chafed wire shorting to ground
- A faulty or defective ECM
- A faulty or damaged digital sensor pulling the shared supply line down
- An intermittent connection issue that only shows the fault under certain conditions (vibration, moisture, temperature)
- The digital sensor supply circuit itself damaged, separate from an individual sensor failure
How to troubleshoot CAT Engine 2634: first checks
- Inspect all connectors on the affected digital sensors (throttle position sensor, coolant level sensor, auxiliary temperature sensor, exhaust temperature sensors, or decelerator position sensor depending on your engine model) for corrosion, moisture, or bent/pushed-back pins
- Check wiring for chafing, pinch points, or exposed conductors that could be shorting to ground or to the engine block/frame
- Verify the ECM connector pins for the digital supply and digital return circuits are clean and fully seated
- Confirm on the electronic diagnostic service tool whether the auxiliary temperature sensor (if equipped) is configured to "Enabled"; if not enabled, the tool will show "Unavailable" for that reading, which is normal and not a fault
- Use a diagnostic service tool to check for any other active sensor diagnostic codes at the same time, since a damaged sensor may accompany this code
- Measure supply voltage at the sensor connector with the harness disconnected from suspect sensors, one at a time, to isolate whether the short is in the harness or in a specific sensor
How the code clears
No separate clearing step is listed. Once the underlying short to ground is repaired and supply voltage returns to normal (either 12.7 volts plus or minus 1.0 volts, or 8.0 volts plus or minus 0.4 volts depending on the system), the code should stop being active. Clear the logged code with a diagnostic service tool and confirm it does not return during operation.
Affected models and serial ranges
2634 appears in our records across 5 CAT Engine models. Match your machine by model and serial number.
| Model | Serial ranges |
|---|---|
| C10 | Serial range not listed in source records |
| C12 | Serial range not listed in source records |
| C15 | Serial range not listed in source records |
| C16 | Serial range not listed in source records |
| C27 | Serial range not listed in source records |
Frequently asked questions
What does CAT fault code 2634 mean?
It means the ECM has detected the digital sensor power supply voltage is below normal, which it interprets as a short to ground somewhere in that supply circuit. This forces all digital sensors on the engine to default values until the fault clears.
Which sensors are affected by code 2634?
Depending on the engine model, this can affect the throttle position sensor, coolant level sensor, auxiliary temperature sensor, left and right exhaust temperature sensors, or the decelerator position sensor. All of these share the same digital sensor supply circuit.
Can I keep running the engine with code 2634 active?
The engine may experience low power while this code is active because the ECM is using default values instead of real sensor readings. It is best to diagnose and repair the short as soon as possible rather than continue operating on default data.
Is the ECM likely to be damaged by this fault?
The digital sensor supply is output short circuit protected, so a short to battery positive or battery negative should not damage the internal ECM circuitry. However, the sensors themselves are not protected from overvoltage, so a short to battery positive could damage a connected sensor.
Why does my diagnostic tool show "Unavailable" for auxiliary temperature?
If the auxiliary temperature sensor has not been configured to "Enabled" on the configuration screen of the electronic diagnostic service tool, the tool will display "Unavailable" for that reading. This is a configuration setting issue, not necessarily a fault.
What is the normal voltage for the digital sensor supply?
On engines using the 12-volt supply, normal voltage is 12.7 volts plus or minus 1.0 volts. On engines using the 8-volt supply, normal voltage is 8.0 volts plus or minus 0.4 volts. The code sets when voltage drops below 11.7 volts or 7.5 volts respectively for at least 2 seconds after the ECM has been powered for 3 seconds.
Does a bad sensor or a bad harness more commonly cause this code?
Both are listed as possible causes. Damaged connectors or wiring in the harness are commonly implicated, but a faulty sensor pulling the shared supply down, or in rare cases a faulty ECM, can also be responsible. Isolating each sensor from the harness one at a time helps narrow down the source.