Case IH 19561 – Engine Control Module (ECM / ECU): SRC Max error for the Linear lambda signal

The voltage signal from the Linear Lambda Sensor (Oxygen or O2 sensor) has exceeded the maximum allowable threshold expected by the controller. This is primarily an electrical circuit fault indicating an open circuit, a short to power in the sensor's wiring harness, or a completely failed internal sensor element.

• Tier 4b
• Farmall 85A
• Farmall 95A
• Farmall 105A
• Farmall 115A
• Puma
• Magnum
• Steiger
• N-Series Loader Backhoes

1. 1

   Visually inspect the Lambda sensor wiring harness for melted insulation, chafing, or breaks caused by exhaust heat.

2. 2

   Disconnect the Lambda sensor and inspect the connector pins for corrosion, moisture, or pushed-out terminals.

3. 3

   Using a multimeter, test the sensor signal wire for continuity back to the Engine ECU, and check for a short to voltage (short to power) or an open circuit.

4. 4

   Check for severe exhaust leaks immediately upstream of the sensor (exhaust manifold and turbo flanges), which can cause extreme lean readings that max out the sensor's logic.

1. 1

   Preparation

   Turn off the engine, disconnect the battery, and allow the exhaust system to cool completely to avoid severe burns.

2. 2

   Clear Access

   Remove any exhaust heat shields or engine bonnet supports that block access to the sensor.

3. 3

   Disconnect

   Unplug the electrical connector for the Lambda sensor from the main engine wiring harness.

4. 4

   Removal

   Using a specialized 22mm (7/8") O2 sensor socket, carefully loosen and remove the sensor from the exhaust bung. Tip: If the sensor is seized, apply penetrating oil to the threads and let it sit before applying force to avoid stripping the exhaust pipe threads.

5. 5

   Preparation of New Sensor

   Check the threads of the new sensor. If it does not have anti-seize compound pre-applied, apply a very small amount of high-temp sensor-safe anti-seize to the threads only. Do not get any compound on the sensor tip.

6. 6

   Installation

   Thread the new sensor into the exhaust bung by hand to prevent cross-threading. Tighten it securely with the O2 sensor socket.

7. 7

   Reassembly

   Reconnect the electrical plug. Ensure the wiring is clipped back into its original retainers so it does not rest against the hot exhaust pipe. Reinstall any heat shields.

8. 8

   Clear Codes

   Reconnect the battery, turn the key on, and use a diagnostic scan tool (like the CNH EST) to clear fault code 19561. Start the engine and verify the code does not return.