P0401 EGR and P0130 Bank 1 Sensor 1 errors - which to replace first, on the off chance that one is creating the other?

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Nov 13, 2017
Hi All, '97 LX450 w/403k miles and no maintenance history before 370k mi. It's been a great vehicle so far.

I'm getting a:

P0401 exhaust gas recirculation flow insufficient detected error, followed by a

P0130 Bank 1 Sensor 1 error (details attached)

Question - What are the chances that the EGR is causing the Bank 1 Sensor 1 alerts? Alternatively what are the chances that the Bank 1 Sensor 1 alerts are causing the EGR errors? I'll buy both Denso O2 sensors and a new EGR, but obviously I'd like to spend as little as possible and not have to return things.

Thanks much for any thoughts.

From my experience/understanding there is no chance of overlap with those two codes.

The PO401 could be caused by any number of components in the EGR system. I wouldn't buy any parts until you test the system and track down where the issue is. The vacuum modulator and egr vsv are two leading sources for issues but clogged vacuum ports/circuits are just as common in my experience. A failed EGR valve is much less common from what I understand. Fortunately for the EGR system you can isolate and test from one component to the next easily once you understand how it works. A vacuum gauge really helps as you can connect it directly to the source ports on the throttle body to make sure you have vacuum there and then work through the vac modulator to the EGR valve and then the EGR VSV. Read up on this forum, search youtube for toyota p0401 troubleshooting, etc. and you should get a pretty good sense of how to test and eliminate the p0401.

My main tip re the p0401 is that you can eliminate the EGR VSV valve from your tests by blocking off that part of the vacuum switching circuit to first confirm that you are getting vacuum at the egr valve when you should. Then you can isolate/test the EGR valve (intro vac. at idle and see if it impacts engine idle speed) and then test the EGR VSV separately (short the connection at the plug and see if the valve opens/closes to vacuum as it should). etc. read up for more info.

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