Exhaust Pressure Sensor Circuit
Exhaust pressure sensor signal is out of range.
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What it means (plain English)
The exhaust pressure sensor measures the pressure in the exhaust system to help control emissions and turbo boost. If the reading is too high or too low, the system throws a fault code.
What the computer is actually seeing
The Engine Control Module (ECM) monitors the exhaust pressure sensor's voltage signal, which should range between 0.5 to 4.5 volts corresponding to the exhaust pressure. If it detects a voltage outside the expected range, it records a fault.
What a healthy reading looks like
0.5 to 4.5 volts for normal exhaust pressure readings; typically around 1-2 volts at idle.
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.
- 11. Inspect the wiring and connector to the exhaust pressure sensor for damage or corrosion. Ensure connections are secure.
- 22. Measure the voltage at the exhaust pressure sensor connector with the engine running. Expect 0.5 to 4.5 volts - use a multimeter for accuracy.
- 33. If the voltage is outside this range, replace the exhaust pressure sensor and retest.
- 44. If the voltage is normal, check for excessive backpressure in the exhaust system (e.g. clogged DPF) using a pressure gauge.
- 55. If backpressure is high, service the DPF or exhaust system as needed.
Common causes
- Wiring issues (damaged, shorted or corroded connections)
- Faulty exhaust pressure sensor
- Excessive backpressure in the exhaust system
- Calibration issues in the ECM
Typical repair cost
$$
Related codes
Frequently asked questions
Is it safe to drive with SPN 1977 active?
It's moderate severity; it’s drivable but should be fixed soon to avoid emissions issues.
Will this return after resetting?
If the underlying issue isn't fixed (like a faulty sensor or wiring), it will most likely return.
Why does this code sometimes pair with SPN 1978?
SPN 1978 relates to the exhaust pressure sensor's performance over time, so both can indicate issues with sensor or exhaust backpressure.
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