SCR SYSTEM PRESSURE SENSOR 1 - SIGNAL BELOW NORMAL
The SCR pressure sensor signal is too low for proper operation.
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What it means (plain English)
The pressure sensor in the SCR system isn't detecting enough pressure, which can interrupt the flow of DEF (Diesel Exhaust Fluid) needed to reduce emissions.
What the computer is actually seeing
The engine control module (ECM) is seeing a pressure reading that is below the expected threshold, typically less than 0.1 volts or a corresponding pressure value below 30 kPa.
What a healthy reading looks like
Expected signal from the SCR pressure sensor should be between 0.5 to 4.5 volts, which corresponds to a pressure range of roughly 30 to 150 kPa.
Guided diagnostic — the DiagCoach way
Don't just throw parts at it. Walk through these in order — each step tells you whether to keep going or stop and fix what you found.
- 1Check DEF fluid level—should be above the minimum level per manufacturer spec.
- 2Inspect wiring and connectors between the SCR pressure sensor and ECM for damage, corrosion, or loose connections—wiggle test is recommended.
- 3Measure the voltage at the SCR pressure sensor connector while the engine is running—it should be between 0.5 and 4.5 volts. If it's out of range, proceed with next step.
- 4Replace SCR pressure sensor if the signal is still below expected values after checking wiring.
- 5Clear the code and test drive the vehicle to see if the code returns.
Common causes
- Faulty SCR pressure sensor
- Wiring issue between sensor and ECM
- Blocked or restricted DEF injector or line
- Low DEF level
- Faulty ECM software
Typical repair cost
$$
Related codes
Frequently asked questions
Is it safe to drive with this code?
It's drivable, but fix soon as it impacts emissions performance.
Will this code come back after I clear it?
If the underlying issue isn't fixed, yes, the code will likely return.
Why does this code sometimes appear with SPN 4818?
SPN 4818 indicates a DEF quality issue, often linked to pressure problems in the SCR system.
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