Slow to heat up

[musttriharder]

Only when the heated seats are switched on.

Thanks so much for all your help so far, but I’m really confused now! If I do a continuity check, this describes my passenger seat, not my drivers seat. Using left and right instead of driver and passenger, a continuity test verifies that everything is connected as it is supposed to be.

What voltage values should I be seeing at the T8s connector as shown below?

Are you saying that, with engine on, switch on, values should be:
Pin 2 12v
Pin 3 0v
Pin 4 12v


T g

 

[Dilbert]

What voltage values should I be seeing at the T8s connector as shown below?

Yes, I have not measured the voltage at pin 2 of T8 in normal operation so I am not sure what you should expect. This is feedback from the thermistor in the seat cushion to tell the control unit the temperature. A thermistor changes resistance according to temperature - the hotter it is , the lower the resistance. I am not sure if it is used to regulate the heat according to the seat switch setting or if it is only a safety cut out.

Does your element sheet kit include the thermistor?

 

[Dilbert]

Just to be sure, these are the connections I am referencing with pin numbers:

 

[musttriharder]

Yes, I have not measured the voltage at pin 2 of T8 in normal operation so I am not sure what you should expect. This is feedback from the thermistor in the seat cushion to tell the control unit the temperature. A thermistor changes resistance according to temperature - the hotter it is , the lower the resistance. I am not sure if it is used to regulate the heat according to the seat switch setting or if it is only a safety cut out.

Does your element sheet kit include the thermistor?

Yep, element includes a thermistor. I’m at a bit of a loss now - Pin 4 has 12v if not connected to the elements. Once connected to the elements, only Pin 2 has 12v and only if seat switched on. Thanks for taking the time to reply - much appreciated

 

[Dilbert]

Can you remind me of the history of your installation. I think you have said you only have one heated seat? Did your van have heated seats or are retrofitting?

 

[musttriharder]

Retrofitting - didn’t have heated seats when I bought the van.

I’ve installed the Kufatec loom - BCM already had pin in A54, so left that out, otherwise followed instructions

I bought T4 elements by mistake, which I assumed was my problem, but I’ve since bought T6 ones and those are the ones I’m using.

 

[Dilbert]

Retrofitting - didn’t have heated seats when I bought the van.

I am not sure what to advise from here. I am not familiar with the upgrade kits. There are a lot of variables involved.

Are you sure the BCM supports heated seats? Is any coding required? I am afraid I do not have the answers but someone on here may.

 

[musttriharder]

I am not sure what to advise from here. I am not familiar with the upgrade kits. There are a lot of variables involved.

Are you sure the BCM supports heated seats? Is any coding required? I am afraid I do not have the answers but someone on here may.

Thanks anyway for all your help and suggestions - I really do appreciate it.

I‘ve had the van apart again this morning and checked the cabling and connections and they’re all good. I’ve checked the J774 8 pin multi plug and I have 12v to pins 3 and 6. Pin 7 (earth) is 0.1 ohms. Pin 2 from BCM has 12v and the seat connections 4 and 8 show continuity to the correct side. Pins 1 and 5 are 0v.
Still get the same values as yesterday, so the only thing I can think is that the relay isn’t working correctly, but I’m reluctant to spend £100 if it isn’t!

 

[Dilbert]

the only thing I can think is that the relay isn’t working correctly

What do mean by relay? What relay?

 

[musttriharder]

What do mean by relay? What relay?

Seat Control Module

 

[Dilbert]

Seat Control Module

Do you have 12V on pin 2 (looks like the main feed in?) of the seat control module when the engine is running, seats switched on and seat elements all connected?

 

[musttriharder]

Do you have 12V on pin 2 (looks like the main feed in?) of the seat control module when the engine is running, seats switched on and seat elements all connected?

13.8 volts at pin 2 of seat module engine running, elements connected, seats on or off

 

[Dilbert]

13.8 volts at pin 2 of seat module engine running, elements connected, seats on or off

And does the 12-13V stay on pins 3 and 8 of the seat control module in same conditions as above?

 

[Dilbert]

Looks like pins 3 and 8 are actually the mains 12V feed to the seat control module. They are fed from a 25A fuse SC27. Make sure this 12V feed is present when on load; i.e. the seat are connected and ON.

The switches for the heated seats go to pins 8 (left seat) and 4 (right seat) on the seat control module. I would assume you should see the voltage change on the relevant pin when you operate the switch. Please also note the temperature sensors (thermistors) in each seat go back to pins 8 and 4 too.

 

[musttriharder]

Looks like pins 3 and 8 are actually the mains 12V feed to the seat control module. They are fed from a 25A fuse SC27. Make sure this 12V feed is present when on load; i.e. the seat are connected and ON.

The switches for the heated seats go to pins 8 (left seat) and 4 (right seat) on the seat control module. I would assume you should see the voltage change on the relevant pin when you operate the switch. Please also note the temperature sensors (thermistors) in each seat go back to pins 8 and 4 too.

Engine on, seats on, elements connected
Pins 3 and 6 are the live feed and have 13.8v, pins 4 and 8 both have 12.6 volts

Engine on, seats off, elements connected
Pins 3 and 6 have 13.8v, pins 4 and 8 have 0 volts

IT‘S MADDENING!!!!

 

[Dilbert]

IT‘S MADDENING!!!!

Just a thought, before condemning the seat control module. Have you definitely got the seat elements wired the right way round? The heat sensor (thermistor) needs to be nearest to the ground return side connection. See circuit diagram above.

If you cannot not physically check, the resistance reading of the thermistor will be the lowest to the correct ground connection to T8s pin3. It will be around 1 ohm higher on the Z6 blue wire (referring to the circuit) and around 2 ohms higher when measured to T8s pin 4.

If it is wired wrong, the feedback to the seat control module will be wrong.

 

[musttriharder]

Just a thought, before condemning the seat control module. Have you definitely got the seat elements wired the right way round? The heat sensor (thermistor) needs to be nearest to the ground return side connection. See circuit diagram above.

If you cannot not physically check, the resistance reading of the thermistor will be the lowest to the correct ground connection to T8s pin3. It will be around 1 ohm higher on the Z6 blue wire (referring to the circuit) and around 2 ohms higher when measured to T8s pin 4.

If it is wired wrong, the feedback to the seat control module will be wrong.

The elements are wired as they came. I’ve measured the resistance with the following results:
T8s Pin 2 -> T2e Pin 2 9.3k ohms
T8s Pin 2 -> T8s Pin 3 9.28k ohms
T2e Pin 2 -> T2e Pin 1 0.9 ohms
T2e Pin 1 -> T8s Pin 4 0.1 ohms

T8s Pin 2 -> T8s Pin 4 9.69k ohms

 

[Grim Reaper]

Do you have access to VCDS? Is there any indication of a fault from the Central Electrics module, like an 02092 fault code?

 

[musttriharder]

Do you have access to VCDS? Is there any indication of a fault from the Central Electrics module, like an 02092 fault code?

Yep - I have VCDS and there’s no error codes. Think I’m going to have to buy another new seat control module as it seems like the only logical failure point now

 

[Dilbert]

The elements are wired as they came. I’ve measured the resistance with the following results:
T8s Pin 2 -> T2e Pin 2 9.3k ohms
T8s Pin 2 -> T8s Pin 3 9.28k ohms
T2e Pin 2 -> T2e Pin 1 0.9 ohms
T2e Pin 1 -> T8s Pin 4 0.1 ohms

T8s Pin 2 -> T8s Pin 4 9.69k ohms

Not sure about these readings. You have 410 ohms difference between the readings on T8s pins 3 and 4 on T8s ??? Should be around 2 ohms; i.e. the resistance of the elements. They also infer that element Z6 is 20 ohms ????