The P1408 trouble code is a manufacturer-specific powertrain code. Its exact definition depends entirely on the vehicle application, primarily indicating an EGR system flow fault, an intake manifold pressure sensor issue, or a secondary air injection problem.
Because it is manufacturer-specific, the exact application must be verified. The code identifies a detected condition, and testing is required to identify the root cause before replacing any components.
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Key Takeaways
- P1408 is a manufacturer-specific code with definitions varying significantly between automakers.
- On Ford applications, it indicates the EGR system flow is out of the expected self-test range.
- On General Motors applications, it points to an intake manifold pressure sensor circuit fault.
- On Volkswagen and Audi applications, it indicates an electrical problem in the secondary air injection system.
- Proper diagnosis requires verifying the exact factory definition and testing the relevant emissions or sensor circuits.
P1408 Code Description and Implications
The P1408 code is a manufacturer-specific powertrain definition. Because it is not a generic SAE code, its exact meaning depends entirely on the vehicle application.
Ford applications: P1408 indicates that the Exhaust Gas Recirculation (EGR) system flow is out of the expected range during the Key On Engine Running (KOER) self-test. The powertrain control module detects that the actual EGR flow does not match the commanded flow.
General Motors applications: On certain GM vehicles, P1408 indicates an intake manifold pressure sensor circuit fault. The engine control module detects an out-of-range voltage or signal from the manifold pressure sensor.
Volkswagen and Audi applications: On these vehicles, P1408 indicates an electrical malfunction in the secondary air injection system. The control module detects an open, short, or performance issue in the secondary air valve or pump circuit.
Common Causes of the P1408 Code
Electrical faults, mechanical blockages, and component degradation are the primary triggers, though the specific causes vary by manufacturer.
For Ford EGR applications: The issue stems from a clogged EGR tube or passages, a failed Differential Pressure Feedback EGR (DPFE) sensor, a stuck EGR valve, or a faulty EGR vacuum regulator solenoid.
For GM manifold pressure applications: The fault is caused by a failed intake manifold pressure sensor, damaged wiring harnesses, or a poor electrical connection at the sensor connector.
For VW/Audi secondary air applications: The issue is caused by a failed secondary air injection pump, a stuck combination valve, a blown fuse, or damaged wiring in the secondary air circuit.
Symptoms Associated With P1408
When the control module detects a fault in these specific systems, it illuminates the Check Engine Light.
Ford applications: You may experience rough idling, engine hesitation, or engine knocking (pinging) during acceleration if the EGR system is not flowing enough exhaust gas to cool the combustion chamber.
GM applications: The primary symptom is an illuminated Check Engine Light. You may also notice poor engine performance or incorrect fuel trims if the manifold pressure sensor provides inaccurate data.
VW/Audi applications: You may hear the secondary air pump fail to run during a cold start, or notice a slight decrease in cold-start emissions performance.
Diagnosing the P1408 Trouble Code
Accurate diagnosis begins by confirming the exact factory definition for your specific vehicle make and model.
Ford EGR diagnosis: Perform a KOER self-test using a scan tool. Inspect the EGR tube and intake passages for severe carbon blockages. Test the DPFE sensor hoses for melting or leaks, and verify the EGR valve holds vacuum.
GM sensor diagnosis: Use a scan tool to monitor the live intake manifold pressure sensor data. Verify the sensor reads near barometric pressure with the key on and engine off, and check the 5-volt reference and ground circuits at the sensor connector.
VW/Audi secondary air diagnosis: Listen for the secondary air pump running during a cold start. Inspect the combination valves for carbon buildup and test the pump relay and fuses to verify power is reaching the pump.
Repairing the P1408 Issue
Repairs must address the specific root cause identified during testing.
EGR and secondary air repair: If EGR passages or secondary air valves are clogged with carbon, cleaning the passages may resolve the issue. If the DPFE sensor, EGR valve, or secondary air pump fails testing, replace the confirmed failed component.
Manifold sensor repair: If the intake manifold pressure sensor signal is out of range and the wiring is intact, replace the sensor. Repair any chafed wires and clear the codes to verify the repair.
Cost Considerations for P1408 Repairs
Cost depends on diagnostic time, component accessibility, required parts, programming requirements, and labor.
Replacing a DPFE sensor or cleaning EGR passages is generally a straightforward repair with moderate costs. Replacing a secondary air pump or intake manifold pressure sensor may require more labor depending on component accessibility.
Prevention Strategies for Future Occurrences
Using top-tier fuel and performing regular intake system cleanings can help prevent the severe carbon buildup that causes EGR passages and secondary air valves to clog.
Inspecting vacuum hoses and electrical connectors near hot exhaust components for early signs of melting or degradation can help prevent circuit faults from developing.
Troubleshooting Tips and Best Practices
Do not immediately replace the EGR valve just because a P1408 code is present on a Ford. A clogged EGR tube, a melted DPFE sensor hose, or a failed vacuum solenoid will produce the exact same flow fault reading.
Always verify the manufacturer-specific definition first. A code that means EGR flow out of range on a Ford means something entirely different on a Volkswagen.
Check for Technical Service Bulletins for your specific vehicle. Manufacturers occasionally release updated DPFE sensor designs or revised EGR tube kits to address chronic carbon clogging issues.
More OBD-II Codes
| P1407 | P1406 | P1405 | P1404 |
| P1409 | P1410 | P1415 | P1416 |
| P1418 | P1420 | P1421 | P1423 |
| P1431 | P1433 | P1487 | P1488 |
| P0016 | P0030 | P0031 | P0050 |
| P0100 | P1151 | P1174 | P1175 |
Frequently Asked Questions
Is P1408 a generic or manufacturer-specific code?
No. P1408 is a manufacturer-specific powertrain code. It indicates an EGR flow fault on Ford, a manifold pressure sensor issue on GM, and a secondary air fault on VW/Audi.
Can I drive my car with a P1408 code?
Driving is generally possible, but performance may be affected. On Ford applications, you may experience engine knock or hesitation during acceleration until the EGR flow issue is repaired.
Will disconnecting the battery clear the P1408 code?
Disconnecting the battery may temporarily erase the code, but it will not repair a clogged EGR passage, damaged wiring, or a failed sensor. The code will return once the monitor runs.
Can a bad catalytic converter cause a P1408 code?
No. P1408 monitors EGR flow, intake manifold pressure, or secondary air injection depending on the make. A catalytic converter efficiency issue triggers different codes, such as P0420 or P0430.
Does P1408 always mean the EGR valve is bad?
No. The code identifies a detected flow or circuit condition. This is frequently caused by carbon buildup, a failed DPFE sensor, or a vacuum leak. The EGR valve should only be replaced after testing confirms failure.
What Should You Do About the P1408 Code?
Confirm the exact factory definition for your vehicle, then follow the applicable manufacturer diagnostic procedure. Because P1408 is manufacturer-specific, the diagnostic path for an EGR flow fault differs entirely from a secondary air injection or manifold pressure sensor issue.
Inspect the relevant system and components, including EGR passages, manifold pressure sensors, and secondary air circuits. Repair any confirmed mechanical blockages or wiring faults, or replace the relevant system components only after testing verifies the failure.
