VOLVO
ECM-251A - Long-term fuel trim. Lower limit
System
Engine Control Module (ECM)
Volvo models this fault code applies to
Applies to the following models:
4 modelsC30 (2007–2013), C70 (2006–2013), S40 (2004–2013), V50 (2004–2013)
Show models by year and engine (5)
What does this fault code mean?
The ECM receives information from the rear oxygen sensor about the mixture at different loads and compares it with the front sensor. If the difference between the sensors becomes too large, so that the rear sensor's adaptation reaches one of its end positions, the code is stored. Here the end position concerned is the lower one. The cause can be either sensor or an air leak in the exhaust.
Possible causes
- Contact resistance, oxidation or poor contact in the connectors
- Air leak in the exhaust system
- Damaged front oxygen sensor
- Damaged center oxygen sensor
- Damaged rear oxygen sensor
What you can do
- 1Read and note the code, clear it and road test to see whether it returns
- 2Check the connectors to the front and rear oxygen sensors for contact resistance, oxidation and poor contact
- 3Look for air leaks in the exhaust system, such as cracks and leaking joints
- 4Look at other stored codes in the control module, since they can show which sensor is faulty and help you avoid unnecessary replacements
- 5Have a workshop replace only the oxygen sensors that the fault-tracing points to
Symptoms you may notice1
- The malfunction indicator lamp (MIL) is on
General guidance for car owners. Diagnosis on the car can point to a different cause.