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1996 Nissan Maxima P0400 Fault: Could Exhaust Leak or EGR Valve Cause It?

Model: 1996 Maxima Fault Code: P0400 Posted: 2007-11-08 20:21

I own a 1996 Nissan Maxima with approximately 205,000 miles. The check engine light is illuminated, and my OBD-II scanner shows the following diagnostic trouble codes: - P0400: Exhaust system leak detected - P0325: Knock sensor malfunction - P1335: Intake air temperature (IAT) sensor issue - P0440: Evaporative emission control system malfunction (additional code, previously unremembered) I am currently focusing on the P0400 code related to the EGR system. The vehicle runs smoothly under normal conditions—sometimes I have to check the tachometer to confirm it's running. Recently, the crankshaft pulley detached from the harmonic balancer, which I have since replaced. During this repair, I removed the crank position sensor (a small black, slightly magnetic component near the crankshaft). I'm now wondering if there is a specific initialization procedure or special steps required to re-install and recalibrate this sensor. Before clearing the codes, when I turned off the engine and attempted to restart within an hour, the car would not start for several attempts—typically after 3–4 brief cranks (about 15 seconds each), it would finally start. This behavior suggests a potential issue with the crank position sensor or its signal. I recently inspected the EGR valve diaphragm and noticed that the vehicle stalled immediately upon removal of the EGR component. I was told at AutoZone that an exhaust leak could be causing the P0400 code, even though standard EGR systems are not typically sensitive to backpressure. Is this plausible? I believe the suspected exhaust leak is located just before the flex pipe under the vehicle—this area has not been thoroughly inspected yet. I plan to repair the exhaust leak, but I’d like to confirm whether an exhaust leak could be directly responsible for triggering the P0400 code. Could it also point to a faulty BPT (Bypass Pressure Regulator) instead? Thanks in advance for any insights or guidance!

Related fault codes

P0400

Comments (5)

Anonymous 2007-11-09 08:17

The 1996 Nissan Maxima does not have a positive feedback EGR system, so an exhaust leak is unlikely to directly cause P0400. Standard EGR valves are designed to operate independently of backpressure. To verify functionality, ensure the EGR valve opens properly and check for vacuum operation in its actuation hose. Please post all diagnostic codes for a complete analysis.

Anonymous 2007-11-09 09:31

The full list of codes I initially saw were: - P0400 - P0440 - P0325 - P1335 After clearing the codes, only P0325 and P1335 have returned after about 30 miles of driving. I reviewed the Nissan service manual via nissanhelp.com—specifically the engine control module (ECM) and ECU sections—and found that the crankshaft position sensor may not be providing accurate readings during the first few seconds of cranking. I will continue monitoring for additional codes as the vehicle completes its driving cycle.

Anonymous 2007-11-09 15:36

For the P0400 EGR issue: Ensure the EGR valve is clean and seated properly within the intake manifold. Verify that it receives vacuum when energized—check for broken or disconnected vacuum hoses. If these are intact, the EGR solenoid may be faulty; inspect wiring for voltage during operation. A non-functioning solenoid could result in a P0400 code. For P0325 (knock sensor): Replacement is likely needed—though it can be costly. The knock sensor failure often occurs due to physical damage or wear. For P0440 (EVAP system): Begin by inspecting the fuel cap and checking for loose or damaged hoses near the fuel tank. These are common causes of EVAP faults. Note: If you replaced the harmonic balancer, ensure proper installation of the crankshaft position sensor ring. Damaged teeth on this ring can cause misreading and trigger a CKP-related fault.

Anonymous 2007-11-10 09:37

Agreed—first priority should be verifying the integrity of both the crankshaft position sensor and its associated toothed ring on the crankshaft. The service manual contains specific test procedures for this component. Physical damage to either part, especially during pulley replacement, could explain intermittent or persistent sensor faults.

Anonymous 2007-11-10 09:57

I tried to avoid spending money initially, but after visually inspecting the crankshaft position sensor, I found that the entire top portion was broken off. This occurred because the harmonic balancer pulley detached and flew off during the repair—hence it's now fixed. I still have P0400 (EGR), P0325 (knock), P1335 (IAT), and a new code: P0136 (rear oxygen sensor). When using a scan tool, the rear O2 sensor only reads 0.010V—this is likely due to poor connection or grounding. I will inspect all wiring today to ensure proper plug-in status. Bonus tip: Joining nissanhelp.com allows free access to one section of the Nissan shop manual per day.