The Caterpillar 3126B uses an electronically controlled HEUI fuel system and an updated ECM platform, which means most operating conditions, faults, and protection events are monitored and stored using Caterpillar diagnostic logic. Error reporting can be displayed in two forms depending on service equipment and vehicle configuration: SAE PID/SID with FMI codes (used with Cat ET and most scan tools), and Caterpillar Flash Codes that can be retrieved without diagnostic software on many chassis.
These diagnostic codes are designed to help identify electrical faults, fuel system problems, sensor issues, low-pressure or high-pressure oil faults, turbocharger and airflow conditions, injector performance, and protection actions such as derate or shutdown. The 3126B ECM records active codes, logged codes, and historical events, including snapshot information, which can greatly speed up troubleshooting.
This section provides a quick-reference overview of both PID–FMI codes and flash-code equivalents, helping technicians correlate OEM dash-lamp sequences with standard electronic diagnostics used in service tooling such as Caterpillar ET, ECAP, Pro-Link, and compatible J1939 readers.
Caterpillar 3126 / 3126B Error Codes
| PID-FMI | Description | Flash Codes |
|---|---|---|
| 00-00 | No Detected Faults | 55 |
| 0001-11 | Cylinder #1 Injector current fault | 72 |
| 0002-11 | Cylinder #2 Injector current fault | 72 |
| 0003-11 | Cylinder #3 Injector current fault | 73 |
| 0004-11 | Cylinder #4 Injector current fault | 73 |
| 0005-11 | Cylinder #5 Injector current fault | 74 |
| 0006-11 | Cylinder #6 Injector current fault | 74 |
| 0022-11 | Primary to Secondary Engine Speed Signal Calibration | 42 |
| 0022-13 | Engine Speed Signal Calibration Not Performed | 42 |
| 0030-08 | PTO Throttle signal invalid | 29 |
| 0030-13 | PTO Throttle out of calibration | 29 |
| 0041-03 | 8 Volt Supply voltage high | 21 |
| 0041-04 | 8 Volt Supply voltage low | 21 |
| 0042-11 | Injection Actuation Pressure output fault | 14 |
| 0043-02 | Key Switch Fault | 71 |
| 0064-02 | Secondary Engine Speed loss of signal | 34 |
| 0064-11 | Secondary Engine Speed no pattern | 34 |
| 0070-05 | Inlet Air Heater current low | 10 |
| 0070-06 | Inlet Air Heater current high | 10 |
| 0071-00 | Idle Shutdown Override | 47 |
| 0071-01 | Idle Shutdown | 47 |
| 0071-14 | PTO Shutdown | 47 |
| 0084-00 | Vehicle Overspeed Warning | 41 |
| 0084-01 | Vehicle Speed loss of signal | 31 |
| 0084-02 | Vehicle Speed signal invalid | 36 |
| 0084-08 | Vehicle Speed signal out of range | 36 |
| 0084-10 | Vehicle Speed signal rate of change | 32 |
| 0091-08 | Throttle Position Invalid | 28 |
| 0091-13 | Throttle Position out of calibration | 28 |
| 0096-04 | Fuel Level voltage high | 50 |
| 0096-06 | Fuel Level voltage low | 50 |
| 0100-03 | Oil Pressure voltage high | 24 |
| 0100-04 | Oil Pressure voltage low | 24 |
| 0101-10 | Very Low Oil Pressure | 25 |
| 0102-03 | Boost Pressure voltage high | 25 |
| 0102-04 | Boost Pressure voltage low | 25 |
| 0102-07 | Boost Pressure not responding | 25 |
| 0105-00 | High Intake Manifold Air Temperature Warning | 64 |
| 0105-03 | Intake Manifold Air Temperature voltage high | 38 |
| 0105-04 | Intake Manifold Air Temperature voltage low | 38 |
| 0105-11 | Very High Intake Manifold Air Temperature | 64 |
| 0108-03 | Barometric Pressure voltage high | 26 |
| 0108-04 | Barometric Pressure voltage low | 26 |
| 0110-00 | High Coolant Temperature Warning | 61 |
| 0110-03 | Coolant Temperature voltage high | 27 |
| 0110-04 | Coolant Temperature voltage low | 27 |
| 0110-11 | Very High Coolant Level | 61 |
| 0111-01 | Low Coolant Level Warning | 62 |
| 0111-02 | Coolant Level signal invalid | 12 |
| 0111-03 | Coolant Level voltage high | 12 |
| 0111-04 | Coolant Level voltage low | 12 |
| 0111-11 | Very Low Coolant Level | 62 |
| 0128-03 | Secondary Fuel Level voltage high | 15 |
| 0128-04 | Secondary Fuel Level voltage low | 15 |
| 0164-00 | Excessive Injection Actuation Pressure | 17 |
| 0164-02 | Injection Actuation Pressure Signal Erratic | 15 |
| 0164-03 | Injection Actuation Pressure voltage high | 15 |
| 0164-04 | Injection Actuation Pressure voltage low | 15 |
| 0164-11 | Injection Actuation Pressure system fault | 39 |
| 0168-02 | ECM Battery Power Intermittent | 51 |
| 0186-14 | PTO Engine Shutdown Switch Occurrence | 47 |
| 0190-00 | Engine Overspeed Warning | 35 |
| 0190-02 | Primary Engine Speed loss of signal | 34 |
| 0190-11 | Primary Engine Speed no pattern | 34 |
| 0224-11 | Theft Deterent Active | 16 |
| 0224-14 | Theft Deterent Active with Engine Cranking | 15 |
| 0231-02 | J1939 Data Incorrect | 58 |
| 0231-11 | J1939 Data Link Fault | 58 |
| 0231-12 | J1939 Device Not Responding | 58 |
| 0232-03 | 5 Volt Supply voltage high | 21 |
| 0232-04 | 5 Volt Supply voltage low | 21 |
| 0246-11 | Brake Pedal Switch #1 Fault | 21 |
| 0247-11 | Brake Pedal Switch #2 Fault | 21 |
| 0252-11 | Engine Software Incorrect | 59 |
| 0253-02 | Check Customer or System Parameters | 56 |
| 0253-14 | Truck Manufacturer Parameter Not Programmed | 56 |
Caterpillar 3126/3126B Engine Error Diagnostic Tools
1. Cat Electronic Technician (Cat ET)
Caterpillar Electronic Technician (ET) is the official OEM diagnostic software used by Caterpillar dealers and many professional shops.
Capabilities:
- Read active and logged fault codes
- View and record engine sensor data
- Clear codes
- Perform calibrations and tests
- Read ECM settings and parameters
- Monitor real-time data (RPM, pressures, temps, etc.)
Requirements:
- A laptop (Windows)
- A Cat communication interface cable (usually part number 185-9756 or equivalent)
- Cat ET software (seasonally updated by Caterpillar)
This is the most complete and reliable diagnostic option for a 3126/3126B for deep troubleshooting, when you need historical codes or logged events (flash codes alone might not capture everything), when diagnosing intermittent faults.
2. Flash Code Retrieval via Dash Lamp (Basic Diagnostics)
Many 3126 engines have a built-in flash code system that will blink the check-engine lamp to indicate a two-digit code without a scanner:
- Turn cruise ON/OFF to OFF
- Press and hold SET/RESUME until the lamp begins to flash
- Count flashes -> interpret code
This gives you active flash codes stored since start-up, but does not show logged codes or detailed data like Cat ET can.
3. Third-Party Diagnostic Tools
There are aftermarket tools that support Cat engines, including the 3126/3126B:
3.1 Jaltest Caterpillar Module
- Covers 3126 and 3126B engines according to tool coverage lists
- Reads diagnostic trouble codes using SPN/FMI codes
- Provides descriptions and troubleshooting guidance
- Can read live data parameters
- Updated regularly
These tools use standard engine datalink protocols and have better coverage than generic OBD tools.
3.2 Innova / Autel / Launch - may read basic CAT codes via SAE J1939/j1587
3.3 Truck/Heavy Duty OBD readers - can sometimes read SPN/FMI codes
They typically don’t support full Cat proprietary features. They may miss parameter details or special tests. They cannot calibrate or program the ECM. So they’re good for preliminary scanning but not full diagnostics.
4. ECM Data Link Adapters
To connect software tools to your 3126 ECM you need one of these typical connection setup:
ECM diagnostic port -> Cat ET cable (e.g., 185-9756) -> USB -> Laptop
Adapters may be OEM Cat or aftermarket (e.g., Nexiq USB Link, MUX interfaces). Make sure the adapter supports SAE J1587/J1939 and Cat protocols.
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