camry p0171 with freeze frame data

[howru]

I got the error code P0171 on my 2000 Camry, 4 cylinder. It translates into system too lean. I have not found any obvious vacuum leak. The freeze frame data reads:

DTCFRZF P0171
FUEL SYS1 CL
FUEL SYS2 N/A?
LOAD_PCT (%) 42.0
ETC ('C) 169
SHRTFT1(%) 10.2
LONGFT1(%) 33.6
MAP (kPa) 12.1
RPM (min) 715
VSS(Km/h) 0
IAT(%) 54


I have erased the code a few times but it came back in a week or a day. When the code is there, I experience hesitation while waiting at traffic stops. This car was having rough idle at cold start but runs fine after warming up.

What could be the problem? This car does not have a MAF sensor, it has a MAP sensor.

Thanks very much for any insights.

[BamZipPow]

How did you test fer a vacuum leak?

Best method to test is using a smoke machine...

[slpr1mz]

have the car running and warmed, lightly spray carb cleaner or another arysole that combusts and drys easily on your vacuum lines. if anything changes in the rpms you got your self a leak. and or make sure your intake doesn't have a break to it. get some electrical debris cleaner and clean your maf.

[fenixus]

your MAP or vacuum line to it is a main suspect. 12.1KPa (or 1.75psi) is WAAAAY to low!
at idle you should be seeing something around 3.6-4.0psi, even more if you use A/C. make sure this value reaches those levels when car is fully warmed up. I'd test the MAP and check its vacuum hose at first.
your car's Manifold Absolute Pressure is the only value which really stands out (except for LOAD_PERCENT and LONGFuelTrim1 that are result of it likely). however bad MAP readings could mean that sensor is operating properly, it's just detecting such bad values (caused elsewhere).

what is ETC? Engine Coolant Temperature (ECT)? what units is that value in? 169 sounds way too high for Celsius (bad sensor likely), but when it was in Fahrenheit then it doesn't look bad and more like a not fully warmed up car on the other hand.
same about IAT, it's supposed to be in temperature degrees (probably same ones as ECT is in), not %, it's the Intake Air Temperature. ... unless it was the TPS (THrottle Position) and this one is supposed to be in %.

please double-check the freeze frame values.

anyways, here are some more hints and descriptions from the FSM:

Fuel trim refers to the feedback compensation value compared to the basic injection time. Fuel trim includes
short−term fuel trim and long−term fuel trim.
Short−term fuel trim is the short−term fuel compensation used to maintain the air−fuel ratio at its ideal
theoretical value.
The signal from the A/F sensor is approximately proportional to the existing air−fuel ratio, and ECM comparing
it with the ideal theoretical value, the ECM reduces fuel volume immediately if the air−fuel ratio is rich
and increases fuel volume if it is lean.
Long−term fuel trim compensates for the deviation from the central value of the short−term fuel trim stored
up by each engine tolerance, and the deviation from the central value due to the passage of time and
changes of environment.
If both the short−term fuel trim and long−term fuel trim exceed a certain value, it is detected as a malfunction
and the MIL lights up.

P0171 - When air−fuel ratio feedback is stable after warming up engine, fuel trim is considerably in error on LEAN side (2 trip detection logic)

Trouble area:
-Air induction system
-Injector blockage
-Manifold absolute pressure sensor
-Engine coolant temp. sensor
-Fuel pressure
-Gas leakage on exhaust system
-Open or short in A/F sensor (bank 1 sensor 1) circuit
-A/F sensor (bank 1 sensor 1)
-ECM

Originally Posted by howru

I got the error code P0171 on my 2000 Camry, 4 cylinder. It translates into system too lean. I have not found any obvious vacuum leak. The freeze frame data reads:

DTCFRZF P0171
FUEL SYS1 CL
FUEL SYS2 N/A?
LOAD_PCT (%) 42.0
ETC (%) 169
SHRTFT1(%) 10.2
LONGFT1(%) 33.6
MAP (kPa) 12.1
RPM (min) 715
VSS(Km/h) 0
IAT(%) 54


I have erased the code a few times but it came back in a week or a day. When the code is there, I experience hesitation while waiting at traffic stops. This car was having rough idle at cold start but runs fine after warming up.

What could be the problem? This car does not have a MAF sensor, it has a MAP sensor.

Thanks very much for any insights.

[howru]

Thank you very much, slpr1mz and fenixus. Fenixus, you taught me car mechanics. I just poured a can of Techron into the gass tank. Still don't know the result. I have bought the vacuum pump and will test the MAP sensor. The ECT (coolant temperature) and IAT sensor are easy to test, so I will test them too. I am also going to test the fuel pressure and replace the fuel filter. With these diagnoisis planned, it sounds stupid to replace the AF sensor, but unfortunately I have ordered it from Ebay. I will update what I found. Thanks a lot.

[fenixus]

if AFR and ECt sensors are more than 100k miles old then you can go ahead and replace them for good measure. as the matter of fact TPS could also be slowly going bad (e.g. fluttering resistance) at that mileage as well. I replaced all of them at 124-130k miles when doing a major tune up on my car.

let me know if you need instructions for testing those sensors, can send you something via PM.

however, by all means, test everything what you can first, before throwing parts at the car. don't assume that each sensor showing weird value is bad, it's an interconnected system.

can you post another freeze frame or double check values of the current ones? some sensor values look odd. edited my above post last night.

also P0171 happens every time car starves for fuel, e.g. when engine dies because of fuel running out. so yeah, checking the fuel pressure and fuel filter is also a very good idea.
techron for cleaning fuel injectors helps too!

good luck!

[howru]

Thnaks fenixus. The current freeze frame data is correct--I mean no typo. I will post another freeze frame later. Yes, this car has 127k on it and parts are getting old. I am planning to off-car clean the idle control valve and EGR valve in some good weather, too.

[JohnGD]

I was looking at the load percentage (42%). If this is calculated based at least partly on throttle body position sensor maybe that should be checked as well? Dunno.

[fenixus]

I know what you mean, it caught my eye too ... but normal engine conditions sheet says anywhere between 19.7% up to 50.4% is ok on 5s-fe, however on mine I usually see only ~27% at idle (around 16% on 1mz-fe)... but then the MAP reading look bad and it could be the part of equation too.

here's what MAP value should be per FSM:
Idling: 20 − 51 kPa
Racing without load (2,500 rpm): 17 − 48 kPa

Originally Posted by JohnGD

I was looking at the load percentage (42%). If this is calculated based at least partly on throttle body position sensor maybe that should be checked as well? Dunno.

[howru]

Today I tested the MAP sensor and IAT sensor, they both look ok. Here is the data:
MAP:
vacuum (in Hg)------voltage drop
0----------------------0 (reading 3.62V)
3.9---------------------0.3
5-----------------------0.5
7.8---------------------0.85
12----------------------1.18
15.5--------------------1.57
19.6--------------------2.2

IAT sensor:
Celcius-------------resistance kOmn
0--------------------4.5
25-------------------2.2
50-------------------0.92
80-------------------0.34
100------------------0.23

Techron seems not working, yestday I got the code back again. Here is another freeze frame:
D7CFR2F---------p0171
FUELSYS1--------CL-Fault
fuelsys2----------N/A
Load_PCT(%)----87.1
ETC ('C)----------165
SHRTFT1(%)-----24.2
LONGFT1(%)-----40.6
MAP(kPa)---------25.7
RPM(/min)--------2014
VSS (Km/h)-------40
IAT('C)------------41

The units of temperature is Celcius degree, so fenixus you are right, ECT looks too high. I am going to test it at another time because I need to drain the coolant.

This time I found there is another code P1130 with P0171. P1130 might be there at the earlier times I just did not pay attention. So the air fuel sensor could be a cause. I am going to change it after I receive the order.
The ECT sensor may well be bad, I will test it soon.
The MAP sensor reading is low, I don't know why, maybe I need to change the air filter or clean IAT and EGR valves?

Thanks.

[fenixus]

this time it seems (when compared to former freeze frame) that your ECT sensor is bad (165 C???). just swap it out, around $5 new oEM from online dealer and go from there.

glad the MAP is OK, it's an expensive part, rarely goes bad though.

changing the air filter is ALWAYS a good idea. how old is your fuel filter though?

I assure you that Techron is doing its job you simply have a root cause elsewhere.

AFR sensors tend to go bad between 100k-150k miles, just get an OE style Denso replacement and swap it out. cheapest to get from amazon, ebay or rockauto ~$100 for and OE AFR.

check your part number here:
http://www.densoaftermarket.com/catalog/

[howru]

I tested the ECT sensor, it looks ok. I just unpluged it and measured the resistance and took the temperature from the radiator cap hole. The readings are:
temperature in Celcius----------------reading (kOmn)
0----------------------------------------6.5
16---------------------------------------2.09
55---------------------------------------0.37
So the sensor is right. It might be my ODBII reader messed up the units in previous readings of the freeze frame data.

So now it may very well be air fuel sensor. I have ordered the OEM Denso part. It should come in today. If it does not solve the problem, I will test the fuel pressure. Will update.

fenixus, I changed my fuel filter about 3 years ago. The air filter was replaced 6 months ago but it was from Walmart and I have a feeling it is not nicely made because it did not fit very well. I replaced my air fuel sensor about 3 years ago when it went bad. At that time I bought it from NAPA online and it might be too cheap.

Thanks.

[fenixus]

you don't know if sensor is entirely right, because you don't know what it shows at operating temperature ~90C (should be around 200-230 ohm). However I agree, preliminary check seems fine.

I don't get why your freeze frames shows 165C on ECT at time of taking it then? maybe there is an intermittent break/problem in wiring somewhere when engine moves while accelerating?

maybe leave ECT for now and swap the upstream AFR first to see if it helps at least the other error code? I'd go with Denso or NGK only on those cars any other brand could cause trouble.

cheap fuel filters are ... well cheap ... go with OEM (comes with bracket for easy installation) or with WIX part. if yours is WIX from NAPA, then leave it, it's probably still good. just double check the fuel pressure at the filter if you have a gauge for that.

EDIT:
can your scan tool monitor LIVE engine conditions while car is idling? can you check what temperature you see on Engine Coolant Temperature?

your P0171 code is caused directly by Fuel Trims (sum of short and long term) hitting over 38%, this trips the code. it's either caused by your bad AFR sensor (P1130 is Air-Fuel Sensor Circuit Range/Performance) or your ECT can mess with it as it impacts ECU job on preparing the A/F mixture.

start with new AFR sensor (glad you took Denso this time) and you need to figure out why ECT can show 165C degrees ... or there are other serious problems like a clog in fuel system or a massive vacuum leak somewhere, both can seriously lean out the system.

[howru]

I replaced the AF sensor. It has been several days and the code hasn't come back. The car is very smooth now, even the rough idle at cold start disappeared. I think the problem is fixed. Thanks everyone.

[fenixus]

check for pending error codes in a few days. it's possible the ECU will throw a code or two still as not all were directly related to AFR sensor. but anyways, good luck, maybe it's all good by now