P0171 - Fuel Trim System Lean Bank 1 - what can cause this code?

Hey all,

I’ve had a couple incidents with my 2001 Grand Caravan (100k miles, 3.3L V6) dropping to about 400 RPM when at a stop sign and then coming back up to normal idle. It never dies and dies normally otherwise, and this has only happened 2 or 3 times.

Tonight when it did it, I happened to get a green light at the same time and started to proceed, and the check engine light came on. Got home and checked the codes, and got the above code (P0171 - Fuel Trim System Lean Bank 1).

What can cause this code to get set? The car has new plugs, wires, O2 sensor (upstream), air filter, recent oil change, and MAP sensor.

The only other issue is that the rad fans aren’t coming on…does anyone know how to get at the fan relay on this vehicle without removing the bumper cover? It’s rivetted to the front bumper.

Thanks guys,


Maybe, the iac (idle air control) valve is sticking, intermittently. It could help to spray some Carb/Throttle Body cleaner into the throttle body bore, let it soak a few minuets, then, run the engine at fast idle until the smoke clears.
What component and circuit tell the engine computer the engine is warm enought to turn on the engine fan(s)? Ans. the engine coolant temperature sensor (cts) and its circuit.

Because only one bank is effected with a lean condition, the first thing to check for is a leaking intake gasket on that bank.


There is only one upstream oxygen sensor, and only one downstream oxygen sensor.
It appears that you have, randomly, been changing parts in the hope that one of them would fix this problem. Now, it’s time to do some troubleshooting. Use the repair manual to check the wiring and the sensors, and actuators (like the idle air control valve, and the egr valve). Use a digital, high impedance, multimeter to do the ohm and voltage checks (Walmart: $25).
Use a vacuum test gauge to test the vacuum on the intake manifold. If the vacuum is low, the repair manual should tell you where it may be loosing vacuum.

hellokit, thanks, I’ll try cleaning the throttle body and check the MAF sensor too.

Would the CTS give a faulty reading to the PCM but still show the coolant temp climbing on the temp gauge on the dash? Also, I checked the fuse and it’s fine (tested it and tried a known good fuse in its place).

Tester, do you mean vacuum leak? How do I check for a leaking intake gasket?

Actually, all those part changes were just regular maintenance (the O2 sensor was done due to it setting a code, the code hasn’t come back, same with MAP sensor).

I’ll check my Haynes manual for doing the vacuum leak tests and sensors.

I use propane to check for intake leaks.

Take a propane torch and remove the nozzle and the check valve below the nozzle. Slip a length of flexible tubing onto the nozzle stem. Start the engine and while it’s idling, slowly open the valve on the propane torch while passing the end of the tubing along the intake manifold seam. If there’s a leak, the engine idle speed will change.


the fan realy which is a Solid State Realy is located on the left chassi rail under the battery, eiasy to observe from underneath than above, costs about $50 and easy to change. Put compure heatsink thermal grease between the back of the re3lay and the frame when attaching the new one.

It has only 1 O2 sensor.

Is this your origianl van?. did anoyonen change injectors in it.

Also “allpar.com” has a forum dedicated to minivans. might get a faster answer there.

Why should the radiator fans come on? Is the engine overheating? If not, the fans are operating correctly by NOT coming on.
If you want to see if the radiator fans will operate, run the engine and switch on the A/C. THEN, the radiator fan(s) should come on.

Thanks for your input, A Murphy. Are you sure about the location of the relay? I see one through the front grill on the front bumper that looks a lot like the picture I found online…Could they have moved it around on different years?

And I’m pretty sure I have an upstream and downstream O2 sensor…

I’m not the original owner, not sure if the injectors were changed.

Yes, it is going above the usual spot on the temp gauge and the fans don’t kick in like they used to. To bring the temp down, you need to keep driving so there is air flow on the rad. It starts to go over temp in stop and go traffic and fans don’t kick in. Also, turning on the heat helps bring down the temp.

I have tried switching on the A/C but the fans still don’t run.

Also, can anybody explain to me how to disconnect the connectors to the fan motors? They aren’t the usual snap-on type, they have a red plastic slider at the top (which I got out), but the connector won’t pull off and I don’t see what’s holding it on…

Disregard, got 'em out (another tab on the back side that had to be pressed down).

Can I hook up my multimeter to this connector during the time when the fans should be running to see if the fan motor is getting voltage? I don’t have wires to run from the motors to the battery directly to test them that way.