Code p1857 - revealed! -

Audi A6 The mid-sized Audi A6 model offers more room to the driver and passengers over the A4 line.

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Old 03-15-2010, 05:44 PM
1st Gear
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Join Date: Jan 2006
Posts: 88
Default Code p1857 - revealed!

Hii and thanks to ( nhusa and a6hcw ) for helping me out. I have know for months that my 98 a6 qttr aha engine has been throwing this code and have searched for hours only to get one dead end after the other. I have had a nonstart since timing rebuild - but had some wierd nonstart issues here and there before i even got into the recent work , which by the way was the end result from a bad $20 themo - and have blamed it on the rebuild itself.
I found this earlier today from a "pay answer" deal that someone else had done and stored in a blog. Hope to see if this is fianllly what's wrong with my ride, and maybe yours if you ever get this frustrating code, and will post results.

P1857 Audi A6 4.2 C5
Submitted: 486 days and 10 hours ago.
Category: Audi Value: $15 Status: CLOSED
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Optional Information
2001 Audi A6 4.2

Already Tried:
We are getting a numbe rof Errors from MAF and Lambda sensors. The car does not idle well and stalls often and will go into limp mode on the Tiptronic. Occasinally the ABS and Traction control lights come on around when the error is occuring. We have ha a couple of garages look at the vehicle and been told the transmission is the issue (makes no sense to me as it stalls in Park)

Posted by Jake 486 days and 7 hours ago. Answer

Thank You for choosing Just Answer for your query. Yes, I can help you.

P1857 / 18265 - Load Signal Error Message from Engine Control. This is a load signl from the MAF Typically the MAF has failed.

To make an accurate speculation I need to know specifically what diagnostic trouble codes (DTCs) are in the Transmission Control Module (TCM) and which DTCs are stored in the Engine Control Module (ECM).

If there are many faults in the TCM, quite often, especially on the 4.2, this vehicle as water intrusion issues. Remove any floor mats and feel the carpet to see if it's wet. The water tends to collect at the rear carpets as this is the lowest point. The TCM is located on the right side, under the carpet, directly in fron of the front seat. If this controller has gotten wet, it is the likely cause for your condition. If caught early, I have had luck drying these units out.

By far the most common cause of an illuminated ABS light along with associated beeps, is a failed ABS control unit. So common if fact that Audi has addressed the matter with a technical service bulletin and a ABS control unit "repair kit", no longer mandating replacement of the complete ABS control unit and pump assembly at about a 50% cost reduction. When this described fault arises the ABS unit can not communicate with the scanner, and blocks the data bus from communicating with the other controllers on the bus. Other times when you have communication it will store a trouble code for a communication problem with the instrument cluster. Both scenarios dictate replacement of the ABS control unit. You must have the vehicle scanned with a VW/Audi capable scanner. If the scanner can not communicate with ABS, or anything else for that matter, try disconnecting the electrical plug for the control unit (left side engine compartment, has all the metal brake lines going to it and one large electrical connector) If you can now communicate with the other controllers the ABS control unit is at fault.

Whether these conditions are separate as described, or interrelated, I do not know. I suggest you check for water intrusion first, then get me the lists of the DTCs, before any further speculation can be made.

I hope I have answered your questions and addressed your concerns, should you have any further questions regarding this matter, please do not hesitate to ask. I want you to be 100% satisfied with my answer.

Positive feedback, referrals and bonuses are always appreciated! If you decide to accept this answer, please click the ACCEPT button by this answer.

Thank You!

Jake "The Audi Doctor"

486 days and 3 hours ago. Reply

I will go and Check for any water. Here are all the DTC from a VCDS Release 8.05


Chassis Type: 4B - Audi A6 C5
Scan: 01 02 03 06 08 15 16 17 18 34 35 36 37 45 55 56 57 65 67 75
76 77

Mileage: 151340km/94038miles
Address 01: Engine Labels: None
Part No: 4D0 907 560 H
Component: 4.2L V8/5V G 0001
Coding: 05752
Shop #: WSC 02325

8 Faults Found:
16518 - Oxygen (Lambda) Sensor B1 S1: No Activity
P0134 - 35-10 - - - Intermittent
16534 - Oxygen (Lambda) Sensor B2 S1: Malfunction in Circuit
P0150 - 35-10 - - - Intermittent
16486 - Mass Air Flow Sensor (G70): Signal too Low
P0102 - 35-10 - - - Intermittent
17546 - Fuel Trim: Bank 2 (Add): System too Lean
P1138 - 35-10 - - - Intermittent
17544 - Fuel Trim: Bank 1 (Add): System too Lean
P1136 - 35-10 - - - Intermittent
17549 - Load Calculation Cross Check: Implausible Value
P1141 - 35-10 - - - Intermittent
17535 - Fuel Trim; Bank 1 (Mult): System too Rich
P1127 - 35-10 - - - Intermittent
17537 - Fuel Trim; Bank 2 (Mult): System too Rich
P1129 - 35-10 - - - Intermittent
Readiness: 0000 0000

Address 02: Auto Trans Labels: 01L-927-156.lbl
Part No: 4B0 927 156 CH
Component: AG5 01L 4.2l5V RdW 1313
Coding: 00001
Shop #: WSC 02325

1 Fault Found:
18265 - Load Signal: Error Message from ECU
P1857 - 35-10 - - - Intermittent

Address 03: ABS Brakes Labels: 8D0-907-389.lbl
Part No: 8D0 907 389 E
Component: ABS/ESP allrad D36
Coding: 06397
Shop #: WSC 02325

1 Fault Found:
18265 - Load Signal: Error Message from ECU
P1857 - 35-10 - - - Intermittent

Address 08: Auto HVAC Labels: 4B0-820-043-MY1.lbl
Part No: 4B0 820 043 H
Component: A6-Klimavollautomat D64
Coding: 00081
Shop #: WSC 02325

1 Fault Found:
01842 - Potentiometer/Actuator for Temperature Flap; Right (G221)
30-10 - Open or Short to Plus - Intermittent

Thanks again


486 days and 3 hours ago. Reply

Just checked the carpets. They are bone dry.



Accepted Answer
OK, looks pretty simple. ALL DTCs are MAF related as I stated the load is a value is a calculated load, based largely on the MAF data.

It's likely a safe bet to fo ahead and replace the MAF, unless you see a problem with the wiring.

If you want to "play" a little more, I suggest you check channel #32. I see you have the Ross-tech VCDS. Here is a great discription of Fuel trims and channel #32 as descibed by Andy at Ross-tech.

Fuel Trim Info

From Ross-Tech Wiki

Understanding Fuel Trim

Some of the most common Fault Codes (DTC's) pertain to fuel trim (rich mixture, lean mixture, etc.) Here is an explanation of fuel trim and what it does for us. The ECU controls Air/Fuel mixture in order to maintain power, efficiency, and emissions. A/F is expressed as either a ratio (14.7:1 for example) or as a Lambda value. With iso-octane ("ideal" gasoline), Lambda of 1.0 is equal to 14.7:1 A/F. This is known as "Stoichiometric", a condition where there is a perfect balance between oxygen molecules and the various hydrogen and carbon based molecules in petroleum. With the oxygenated gasoline that most of us use, actual A/F ratio of 15:1 is closer to stoichiometric.If Lambda is greater than 1.0, then there is a surplus of air and the engine is running lean. If Lambda is less than 1.0, then there is a surplus of fuel and the engine is running rich. It should be noted that the ratios are mass-based, not volume-based.

So, why don't we always run at 1.0 all the time? Well, we do MOST of the time. At cruise and idle, mixture is held tightly to 1.0 to keep the catalytic convertor at optimal efficiency, so the emissions are minimized. However, when we need acceleration, the mixture gets richer. Why? Maximum power is made between 0.85 to 0.95 Lambda (12.5 to 14.0 A/F with iso-octane). So, under acceleration, mixtures get richer. Sometimes you want to get even richer under acceleration to keep detonation (pre-ignition of the mixture from excess cylinder temperatures) away. The 1.8T has a relatively high compression ratio for a turbocharged engine, which especially under lots of boost, is very succeptible to detonation).

So, now that we know that the ECU wants to be able to control the A/F ratio. It has a prescribed set of values (maps) for a given RPM, Load, etc. So, the ECU tells the injectors to pulse for exactly XX.X milliseconds and that SHOULD get us the proper A/F ratio that we want. Well, if you tell an employee to go do something, you want to make sure they actually did it, right? The ECU has some snitches (the front O2 sensor and the MAF, for the most part) that will report back whether or not the desired mixture has been attained. The rear O2 sensor is used mostly to monitor the condition of the catalytic convertor, although in some applications it also contributes to trim information.

Based on feedback from the snitches, the ECU learns to apply a correction factor to its commands to the fuel injectors. If you know that your employees take longer than the standard allotted time to do a specified job, you will need to adjust for that in your planning (injectors are in a union, so it is tough to fire them ). The learned values go between the maps in the ECU's Flash ROM (the "chip") and the signal to the fuel injectors. These learned compensations are known as "trim". So, when you see "trim", it means "compensation".

"Add" means additive trim, which is addressing an imbalance at idle. When the ECU is using additive trim, it is telling the injectors to stay open a fixed amount longer or shorter. The malfunction (e.g. vacuum leak) becomes less significant as RPM increase. For additive adaptation values, the injection timing is changed by a fixed amount. This value is not dependent on the basic injection timing.

"Mult" mean multiplicative trim, which is addressing an imbalance at all engine speeds. The malfunction (e.g. clogged injector) becomes more severe at increased RPM. For multiplicative adaptation values, there is a percentage change in injection timing. This change is dependent on the basic injection timing.

You can check your current state of trim by using VAG-COM or equivalent to look in Group 032 (in many modern ECU's, consult your Factory Repair Manual for the specific group for your particular vehicle) in your engine measuring blocks. The first two fields will have percentages. The first field tells the fuel trim at idle (Additive). The second field tells the fuel trim at elevated engine speeds (Multiplicative). Negative values indicate that the engine is running too rich and oxygen sensor control is therefore making it more lean by reducing the amount of time that the injectors are open. Positive values indicate that the engine is running too lean and oxygen sensor control is therefore making it richer by increasing the amount of time that the injectors are open.

It is totally normal for both the first and second fields to be something other than zero. In fact, zeros IN BOTH FIELDS indicates that either you just cleared codes (which will reset fuel trim values) or something isn't working properly. If values get too far away from zero, it will cause a DTC (fault code) and can set off the MIL (commonly referred to as the Check Engine Light, or CEL). Specifications for normal operation are usually somewhere near +/- 10%.

In general, an out-of-spec value in the first field (Additive) indicates a vacuum leak since it is mostly present at idle, when vacuum is highest. An out-of-spec value in the second field (Multiplicative) indicates a fault at higher RPM, and may point to a faulty MAF.

Here's a good sanity check for the status of your MAF. Do a full-throttle run all the way to redline in a single gear (second works fine). Group 002 usually shows air mass in g/s (in many modern ECU's, consult your Factory Repair Manual for the specific group for your particular vehicle). Your peak airflow should be roughly 0.80 times your horsepower. So, if you have a stock 150 hp 1.8T, expect around 120 g/s. If you see significantly less than that, you MAF may be on the way out. This still works if you are chipped, but "race" programs may make more power through timing, rather than airflow. Therefore, take all readings with a grain of salt.

Andy 10:45, 26 January 2006 (Eastern Standard Time)

Thank You!


Expert: Jake
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486 days and 2 hours ago. Reply

Thanks for the Response. I will test that and see what I get. We will replace the MAF and go from there.

Thanks Again


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Old 03-02-2011, 05:21 PM
1st Gear

Join Date: Jul 2010
Location: Colorado
Posts: 14

Thank you so much for this information. I got my car scanned yesterday for codes, the big one was 18265 (ECU), my mechanic couldn't find any information on it and said I would probably have to go to the stealership. The MAF code was coming up, it was too low or something like that. My ESP light has been stuck on for a while and traction control does not work. I am going to try to replace the MAF sensor and hopefully it will fix it! Thanks again.
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18265, 2001, a4, abs, audi, code, control, engine, error, load, message, module, p1857, signal, vw

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