[Trailmixx]

Hi guys,

So, I have a 98 Frontier just failed smog (high NOX) I also have a check engine code - "P0500 A" speed sensor code.

This is what I've done :

New plugs/wires, Cap/rotor, 02 sensor, air filter, fuel filter. Started with the easy stuff.

I bought an ERG valve (not replaced yet) and Speed sensor (that mounts to the transmission not replaced yet)

2 questions - 1) does the P 0500A speed sensor code mean it is the sensors located on the wheels or the one on the transmission? 2) How do I test the ERG valve to make sure its even bad? 2a) and how do I know which catalytic converter is bad if at all? The one off the intake or the one down by the muffler? The intake manifold one is like $700 !!!

I know it's a lot of questions, but if anybody has the knowledge to share I would really appreciate the help. I'm still learning !

Thanks in advance.

 

[smj999smj]

P0500 could mean the vehicle speed sensor in the trans is faulty or it's driven gear is bad, the speedometer head....which is part of the integrated meter assembly (the "cluster), the circuit between the sensor and the cluster or even the drive gear inside the transmission, albeit rare. There have been a lot of cluster problems in the early Gen1 Frontiers. The vehicle speed sensor generates about a volt per 10 mph; you can monitor the voltage using an A/C voltmeter at the back of the cluster to check the sensor output and circuit.

You can component test the EGR valve using a vacuum gauge to it; you should be able to apply vacuum to it using a vacuum pump, which should cause the engine to run rough while idling.

If you don't have P0420 or P0430 trouble codes, I wouldn't assume that the converters are bad. The upstream converter is the one that is monitored and usually fails, if one of them does fail.

High NOx emissions indicate a lean condition. A stuck open EGR valve could do this, but so could anything else that would cause such a condition. Intake gasket or other leaks, low fuel pump pressure, faulty Mass Air Flow sensor, faulty upstream oxygen sensor, to name a few example.

 

[Trailmixx]

To add : my speedometer is intermittent

 

[smj999smj]

Well, like I said, there were a lot of failures with the clusters in early Gen1 Frontiers. Most of them are discontinued by Nissan, but there are a number of places that repair them. Mr. Whizard is one of those companies:

Speedometer Repair | Instrument Cluster Repair | Odometer Repair | Mr. Whizard

 

[Trailmixx]

Thanks man I appreciate all the help I'm getting closer to feeling like I know what to do