R129 Gearbox Issue

[Brendan 229]

Hi Everyone, I'm looking for a little advice, I have 1999 SL320 R129, This car is my pride and joy and only gets driven in the summer doing maybe just 2000 miles max, unfortunately I haven't driven if for the last three years. I usually garage the car come October and bring her out again at Easter ready for the summer. I normally start her up and drive down to the garage and get it MOT, a mere formality every year. Three years ago when I stared it up, all was good, I let it warm up and then set off to the garage but within a couple of hundred yards I knew there was an issue. The best way I can describe it is, if the car had a manual gear box you would normally change up from second to third at about 25-30mph, but unfortunately my car wont change up, it just over revs. it doesn't go into limp mode we just don't go anywhere in a hurry. It passed the MOT and I drove home the two miles at 25 mph. I've replaced the oil hoping that might make a difference but since that day I haven't driven it so I need to get it sorted so I can enjoy it again.
I've called several Automatic gearbox companies looking for help but know one gas any idea saying get it here and we will strip it down to see what the problem is. Hmmm... The only one that inspired me was a company based in Dagenham called JT automatics who said it was the Speed Sensor / Conductor plate". So a two part question, know the symptoms that I described would you say he is correct? and does anyone have any recommendations on a good garage that I can take it to a bit more local and wont rip me off.

Thank in advance for your help and advice

 

[ajlsl600]

Wud hav thought some trans related fault code wud show up I guess?? You have the old round diagnostics socket under the bonnet?

 

[Brendan 229]

Wud have thought some trans related fault code wud show up I guess?? You have the old round diagnostics socket under the bonnet?

Thanks for the reply but I don't have a scanner and no idea on the shape of the diagnostics port, do you have a picture so I know what to look for?

 

[ajlsl600]

Your car does not have a 16 pin OBD port. It uses the MB 38 pin connector under the bonnet. For basic engine diags you MAY be able to use a 38pin to 16 pin adapter cable (works on my 2001 E Class) but if your car is too early even that won't work and you'll need a blink


Copied from lk post. Round socket with a black top rear right of eng

 

[rich.g.williams]

Can you confirm what type of automatic transmission is fitted? If its the 5Gtronic 722.6 five speed then your fault description sounds like the transmission is stuck in so called limp mode, maybe you notice quite a clunk when engaging Drive (from Neutral) yes?

 

[Brendan 229]

Can you confirm what type of automatic transmission is fitted? If its the 5Gtronic 722.6 five speed then your fault description sounds like the transmission is stuck in so called limp mode, maybe you notice quite a clunk when engaging Drive (from Neutral) yes?

Hi Rich, I wouldn't have a clue on the type, whatever comes as standard on the SL. Ironically I do get a clunk as you say but the car doesn't go into limp mode, I could drive quicker but it just over revs and so

 

[rich.g.williams]

I found this on the net "1999 Mercedes Benz SL320 is a great example of the R129 model..... Its 3.2-litre V6 engine produces around 221bhp, and is coupled to a five-speed automatic transmission"

As a 1999 V6 it most likely has a five speed 722.6 transmission.

Well as I said if you have only one forward gear (2nd gear) and the clunk when you set off then the transmission is in a limp mode (not the engine).

I'm assuming that you are saying that the car is stuck in only one gear yes?

Means that the transmission computer has experienced a fault condition and put itself and the transmission into a safety limp mode where nothing happens as regards gear shifts.

Suggest read codes or get codes read by specialist, hopefully its a straightforward problem in the electrics that control the transmission.

If you search 722.6 transmission or 5-speed G-tronic transmission etc you will find a lot of info on this forum.

 

[Brendan 229]

I found this on the net "1999 Mercedes Benz SL320 is a great example of the R129 model..... Its 3.2-litre V6 engine produces around 221bhp, and is coupled to a five-speed automatic transmission"

As a 1999 V6 it most likely has a five speed 722.6 transmission.

Well as I said if you have only one forward gear (2nd gear) and the clunk when you set off then the transmission is in a limp mode (not the engine).

I'm assuming that you are saying that the car is stuck in only one gear yes?

Means that the transmission computer has experienced a fault condition and put itself and the transmission into a safety limp mode where nothing happens as regards gear shifts.

Suggest read codes or get codes read by specialist, hopefully its a straightforward problem in the electrics that control the transmission.

If you search 722.6 transmission or 5-speed G-tronic transmission etc you will find a lot of info on this forum.

Thank you so much

 

[Wearsafoxhat]

Probably a good time to get the codes read and proceed from there.
Your car is likely to have the 38 pin diagnostic port in the engine bay, passenger side under a round cap.
An iCarsoft MB 2 with a red 38 pin to 16 pin adaptor can read the majority of codes on a 129 if you fancy having a go yourself. Speak to the guys at UKParts direct and helpful to get the 16 pin obd extension lead too.

 

[rich.g.williams]

Any code reader will read the codes likely affecting your transmission. Plenty on eBay for a few pounds, 38 pin connector under the steering wheel

 

[LostKiwi]

Any code reader will read the codes likely affecting your transmission. Plenty on eBay for a few pounds, 38 pin connector under the steering wheel

No it won't.
You need the correct kit.
You can read engine codes using a generic code reader but not gearbox or any other module.

 

[rich.g.williams]

No it won't.
You need the correct kit.
You can read engine codes using a generic code reader but not gearbox or any other module.

The likely 722.6 transmission fault codes are passed to and included in the OBDII specification and I have seen them myself so yes any straightforward OBDII code reader will read the 722.6 transmission codes. As I was saying "any code reader will read the codes likely affecting your transmission. Plenty on eBay for a few pounds, 38 pin connector under the steering wheel"

I was trying to answer Brendan's original question, I don't think he want's to do the repair himself or fork out for an expensive 38 pin 16 pin code reader.

 

[rich.g.williams]

The only one that inspired me was a company based in Dagenham called JT automatics who said it was the Speed Sensor / Conductor plate

Brendan yes I agree with what JT Automatics told you. That it is likely the Conductor Plate (easily accessible and has the speed sensors on it), also possibly the electrical wiring associated with the transmission or the electrical solenoids not a major mechanical failure.

I can't say if JT Automatics are any good but I had a look at their website and the website is very detailed very good. I'm not suggesting you need a new transmission (far from it) but I found a price for a complete new transmission on the JT website as follows:-

TRANSMISSION TYPE ________GEARBOX PRICE____TORQUE CONVERTER_____REMOVE & REFIT____FLUIDS_____TOTAL INC VAT
5 SPEED W5A330 (722.6)_____£1,295____________£290__________________£250_____________£200_______£2,442.00

JT Automatics deal with several manufacturers which is not a bad thing because the 722.6 transmission is ubiquitous it is fitted to many models of Mercedes cars, Mercedes vans, Jaguar cars, Porche cars and in the US it is fitted to Chrysler and others.

 

[rich.g.williams]

Any code reader will read the codes likely affecting your transmission. Plenty on eBay for a few pounds, 38 pin connector under the steering wheel

To be more correct the OBDII connector is the rectangular 16 pin connector. The 38 pin connector is round, in the engine compartment and can also be OBDII. 1999, 2000, 2001 is when Mercedes were switching from the 38 pin to the 16 pin so most likely both are there.

My 16 pin OBDII code reader:-



Cost a few pounds and works with an app on my phone.

 

[LostKiwi]

The likely 722.6 transmission fault codes are passed to and included in the OBDII specification and I have seen them myself so yes any straightforward OBDII code reader will read the 722.6 transmission codes. As I was saying "any code reader will read the codes likely affecting your transmission. Plenty on eBay for a few pounds, 38 pin connector under the steering wheel"

I was trying to answer Brendan's original question, I don't think he want's to do the repair himself or fork out for an expensive 38 pin 16 pin code reader.

On the 38 pin diagnostics connector each pin corresponds to a control module.
The 38 pin readers are aware of this and query the individual pins. Generic code readers only query a single pin on an adapter (usually pin 4) so cannot read the codes in the TCU which is on pin 10.

 

[rich.g.williams]

On the 38 pin diagnostics connector each pin corresponds to a control module.
The 38 pin readers are aware of this and query the individual pins. Generic code readers only query a single pin on an adapter (usually pin 4) so cannot read the codes in the TCU which is on pin 10.

That was the old system where dedicated controllers such as the EGS52 Transmission Control Module used a single wire to communicate diagnostic information and this single wire was piped along (from main electronic controllers) to the round 38 pin connector.

As this was going on firmware designers were using this one wire protocol and putting their diagnostic data onto the Can Bus. Essentially all modules on the Can Bus (or Buses) talk to each other and a diagnostic code reader connected to diagnostic 16 pin connector can talk to all modules, look for real time data and ask for fault codes. OBDII specifies a list of fault codes that a car Manufacturer must make available by law via the 16 pin diagnostic connector. The CAN bus is something like USB but is optimized for controllers and allows several controllers to connect to the same CAN bus. It stands for Controller Area Network.

Its not worth getting excited about the EGS51 and EGS52 generation of transmission controller diagnostics its not the holy grail of diagnostics. Yes they pass diagnostic codes but the way they collect diagnostic information is quite crude. For example they diagnose solenoid faults simply by checking for short circuit or open circuit fault to each solenoid. They look for implausibility errors also by comparing engine speed, two internal gearbox speeds and wheel speed. In some ways they lack common sense diagnostics. For example it would help greatly if the TCU checked speed sensor ratios more carefully.

Generic code readers read the CAN bus OBDII protocol and the OBDII specification includes transmission fault codes.

 

[rich.g.williams]

Explanation of OBD-II diagnostic trouble codes (DTCs)​

Before DTCs became commonplace, diagnosing issues could be time-consuming. With OBD-II, vehicles can basically monitor themselves and alert drivers to potential problems using indicator lights. These indicator lights identify things like:

• Engine temperature warning
• Tire pressure warning
• Oil pressure warning
• Brake pad warning

Some indicator lights indicate multiple problems. For instance, the brake system light could suggest that the parking brake is on, the brake fluid is low, or that there is an antilock braking system (ABS) issue.

The check engine or malfunction indicator light (MIL) tells you that the vehicle’s computer has set a DTC, requiring a diagnostic tool to read.

A DTC comes in a string of five characters. So, for example, you might run into a code that says P0575. Let’s examine what each of these characters tells us.

• The first letter tells us which of the four main parts is at fault.
• • P = Powertrain
  • B = Body
  • C = Chassis
  • U = Network
• The second tells us whether we’re looking at a generic OBD-II code or a manufacturer’s code. (If a manufacturer feels there isn’t a generic code covering a specific fault, they can add their own.) A zero denotes a generic code.
• The third character alerts us which vehicle’s system is at fault. Codes include:
• • 1 = Fuel and Air Metering
  • 2 = Fuel and Air Metering (injector circuit malfunction specific)
  • 3 = Ignition System or Misfire
  • 4 = Auxiliary Emissions Controls
  • 5 = Vehicle Speed Control and Idle Control System
  • 6 = Computer Auxiliary Outputs
  • 7, 8, 9 = Various transmission and Gearbox faults
  • A, B, C = Hybrid Propulsion Faults

• The last two characters tell us the specific fault. These help pinpoint exactly where the problem is located and which part needs attention.

So in the case of P0575, we know that it’s a generic OBD-II powertrain fault. We also know that the specific fault relates to the vehicle speed control or idle control system. By consulting the list of OBD-II codes, we discover that it’s a problem with the cruise control input circuit.

There are more than 5,000 ODB-II and manufacturer-specific codes. Thankfully, you don’t have to memorize these, but you’re bound to see some codes often enough to recognize them.

 

[LostKiwi]

I had a 2001 E Class. 38 pin. It reported nothing but the engine to a generic reader.

 

[alexanderfoti]

Back to the ops issue.

As above. Likely to be a speed sensor fault, but also likely is a faulty selector module. Get it to a merc specialist not a gearbox specialist and they will have it diagnosed within the hour.

 

[Brendan 229]

Thank you everyone for your replies, I have had someone do a OBM 2 test for me with the reading stating the following, so not really any more the wiser so now booked into my local Independent Mercedes garage, I’ll advise when I get it up and running again.
1). Modulating pressure control valve ???
2). Shift Lever Coding is Sporadically invalid ???