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code help

1987 3.8L thunderbird.  I pull a 31 & 41 code.  Any help where to start trouble shooting the EGR?

code help

Reply #1 –
All you ever wanted to know about EGR is here.

With regards to code 31. I believe that is caused by a low voltage condition. Offhand, I'd say it is probably a wiring issue or a bad EVP sensor.
I'd start by making sure the EGR functioned. Check for operation by giving the engine some throttle in park while warm.
If the EGR doesn't actuate, test the valve diaphragm and the solenoids.
Assuming it does function, back probe the EVP SIG and SIG RTN wires and (key on) note the voltage wrt vacuum. Check the results with the table from the Tomco site. (Link)

The 41 is most likely a bad O2 sensor.

code help

Reply #2 –
It is sometimes helpful to know the source of the codes.

KOEO code. It is either an "on demand" or a "continuous" code. Continuous code is also called Memory code.

KOER code.

Code 31, the EVP (Egr Valve Position sensor) voltage may be too low when the valve is closed.
On my '84 T-Bird I put a needle through the BR/LG wire at the EVP.
Between the needle and the battery - I have 1.06V with the KOEO and 1.08v with the engine running.

My ref voltage on the O/WT wire is 5.09v.

When I run the KOER test the voltage steps up to 1.56V and back down to 1.08v.

The shop manual pinpoint test says it must be greater than 0.5v and less than 1.25v when the valve is closed.
 

code help

Reply #3 –
Continuous (Memory) code 41: (Right) Oxygen sensor is not switching. Lean indication.

KOER code 41: (Right) Oxygen sensor signal lean during self test.

(Right) If you have two O2 sensors it's the right side thats failing.