PEUGEOT BOXER III - Repair of the AdBlue tank PEUGEOT BOXER III, CITROEN JUMPER

Amazing job, full reverse engineering. Super that you managed to write down so much useful information.
I have just pulled the tank off after the P20E8 fault (Peugeot Boxer III). I have tested everything, obviously the thermistor on the heating plate is faulty (400 ohm).
Thermistor already ordered.

While pulling the tank I measured the resistance on the heater plug of the wire to the injector, it looks like there is a break. Can anyone have an idea of when this circuit is checked by the controller? Is there a possibility that until winter comes I won't see the error? Is it possible to replace this heater with some kind of resistor, if so, what kind?

the system diagnoses itself and, if there is a break in the heating system, it would indicate this with a message on the dashboard, or perhaps it is not the thermistor but the heater that has gone wrong.

The thermistor is 400 ohm and does not respond to temperature change. It looks like there are two faults, but I wonder if the external heater to the injector is always tested and if the system will trip if there is a break in this heater.

is tested by the system, plug in the didgibox and see what adblue hurts.

I checked with Launch, only one error P20E8 (low AdBlue pressure). After clearing the error and turning the ignition, you can hear the pump come on and initially there is no error. Pressure 4 bar (i.e. none), urea temperature 0°C, Operating Status Of The Denox System: Pump Stopped Empty. After driving a few kilometres, when it comes to AdBlue, the error appears, while nothing changes in the parameters. It looks as if there are some default parameters on the ECU that are not being updated, which is probably because the AdBlue is cut off early on. A couple of things are unclear to me: if a test is done when the ignition is turned, why does the error not appear immediately but only after some time, is this always the case or does it depend on the fault. The second thing is: if the ignition is turned on, should the pump build up a pressure of more than 4 bar? Does the pressure only build up while driving? And one more thing: if an error appears on the dashboard, there is no error in the ECU when I connect the interface, only I have to drive around a bit more and the message "Engine error" appears, and only then can I see the error in the ECU - is this normal?

The urea temperature of 0stC and the resistance of the thermistor indicate that the thermistor is defective. This should be done in the first instance.

After replacing the thermistor and putting a 3.3 ohm resistor on the heater circuit of the urea wire (just as a test), unfortunately it still doesn't work. The only thing that has changed is that it now shows the real temperature instead of 0°C. Does anyone know if DiagBox allows you to see some more detailed errors from the AdBlue module itself?

can someone help me about transistor that is burn?


First is CG p?😕

Please help me!

>>21904267
Problem is thorn membrane, replacement?

Good morning
I also respect what the author has done for the benefit of all AdBlue car owners . I read the thread from cover to cover and even felt like a bit of an electronics expert, as I understood some of it, but I’m still in a bit of a quandary. To start with... I bought a 2017 Peugeot 308, drove it for just 3,000 km and now I’m having problems with the AdBlue... I have a Diagbox and, to be honest, I was looking for this problem in the fault history, as I had the impression that I was about to find evidence that the previous owner had cleared the faults and sold the car, and I would have a chance to claim under the warranty for hidden defects... but... the Chinese Diagbox displays what is probably the most common error among AdBlue faults, namely P20E8, but the error history shows something completely different... saying something about a missing catalytic converter... It’s a bit odd, but the AI says this is possible in Chinese clones... So, with the P20E8 error, not immediately coming across this forum, I thought of the thermistor, as, like with most systems, it shows the fluid temperature as ‘0’. I haven’t removed the reservoir yet, but if it is that 10 kOhm thermistor, is my concern about it justified? After all, this original thermistor also acts as a thermal fuse, doesn’t it? Is there another thermal fuse on this heating board? The AI is still stupid enough to contradict itself when I ask it about this. Are there two temperature sensors in the tank, or is there one that measures the fluid temperature from a slight distance, whilst the one on the heating plate is only there to measure the heater’s temperature and, say, send a signal to switch it off at 180°C? If I slide a new one into the conduit, it won’t be positioned like the original and won’t fulfil that role; it will certainly have much greater thermal inertia. Is there definitely no risk of the tank melting – or, in the worst case, the car catching fire?

Check the resistance of the current thermistor with an ohmmeter; it’ll probably be around 300 ohms.
That’s what I did: I cut it off, soldered on a new one and pushed it into the tank as far as it would go. I’ve checked the temperature many times since then and it seems to be correct. I’ve been driving like this for two years now and the problem hasn’t occurred. Recently, I’ve had two AdBlue-related faults – P21C5 and P2A00 – but they don’t cause the check engine light to come on in the car and the AdBlue seems to be working properly. After clearing them, they don’t reappear for a while, so I’m not too worried about it.

>>21921100
So you got through one winter and some freezing weather like that? I still think the main risk is winter, and that the heater won’t switch off at the right moment, so there’s a risk it’ll either burn out or start melting the tank? Does the heater start heating at, say, -1°C or at the AdBlue freezing point of ~ -11°C? Perhaps if you garage your car and live, say, in southern Poland, you didn’t have such a winter and the heater didn’t really need to work, unlike us in Mazovia, where temperatures dropped to -22°C at times, and it would have been running at full power, and then who knows how it would have worked... If that thermistor on the heater acts as both a control and a safety feature, then... I suppose I’d have to look for a working bottom section of that tank somewhere on Allegro or send it off to be cut open and reconditioned ;/. I think you need to think about this after all, because maybe nothing will happen in the garage whilst it’s parked, but if the tank were to melt or even catch fire somewhere on a long journey... then the 3,000 zł saved on the tank would unfortunately go down the drain.

Oh, and you write: “I checked the temperature”, so you checked the coolant temperature in the tank with a diagnostic box to see if it was showing a reasonable reading, right? But here’s the thing: is that thermistor only there for that? If there are actually two in the tank, then perhaps the second one shows the fluid temperature, and since this one is directly on the heater, if it started heating up, it wouldn’t be showing the fluid temperature, because it would display a value of, say, 120°C at that specific point, and the soldered-in one will never work like the original, because it isn’t directly on the heater, so there’s thermal inertia – by the time it registers that the heater is at 150°C, the motor might already be at 220°C and burn out, for example. I’m not entirely sure how it works; I suppose these two sensors compare the temperatures with each other and the data goes to the microcontroller? Of course, it would be great if this repair method were permanent and effective, but I have my doubts.

I live in the south, near Kraków. We didn’t have a mild winter, and temperatures did drop to -20°C. In such freezing conditions, I try to keep my car in the garage, but at work it’s parked outside, so I couldn’t avoid the cold. From what I’ve read, I’m not the only one who did this, and nobody has mentioned any problems.
If you’re worried, get in touch with Bluefix’s Dawid Broniszewski – he repairs these systems in Jaworzno, has very good reviews and reasonable prices.

>>21921115 OK, I think I’m starting to get the hang of how it works… I reckon Gemini AI has really helped me out here, I could paste it here, but I think I’d be cluttering up the forum, so I’ll just paste a snippet – but it makes sense, i.e. that component on the heater isn’t actively involved in controlling it, which is why soldering in a resistor or thermistor ‘works’.

Gemini:

The component you’re asking about (a distinctive, elongated, metal part soldered directly onto the flexible or rigid heating plate in PSA Group – Peugeot/Citroën – AdBlue tanks) is a thermal fuse (thermal cut-out), not a temperature sensor.

Here is a detailed explanation of its role and the difference between these components in this specific system:

1. What is this component responsible for?
It is a reusable (bimetallic) thermal protection device or a single-use thermal fuse. Its main task is to protect the plastic tank and the heating mat itself from melting or fire in the event of a controller failure.

If, for any reason (e.g. a relay malfunction or software error), the system were to supply a continuous current to the heater, the temperature could rise to a dangerous level. When the temperature exceeds a certain threshold (usually around 70–80°C), this fuse disconnects the heater’s power circuit, cutting off the current supply.

2. Why is this NOT a temperature sensor?
Temperature sensor (NTC/PTC): Used to continuously measure the fluid temperature and transmit this data to the controller (indicating, for example, whether the fluid is at -5°C and the heater needs to be switched on, or whether it is already at +15°C and can be switched off). In PSA tanks, the temperature sensor is usually a tiny, black or blue component (often a drop-shaped thermistor) soldered onto a different part of the board or integrated directly into the wiring harness/level sensor.

Thermal fuse: Operates on a binary basis (closed/open). It does not measure the temperature value, but merely reacts to a critical rise in temperature.

A common problem in Peugeot / Citroën cars (error P20C2 and related)
This component is very often damaged by corrosion (AdBlue fluid is extremely corrosive and penetrates the circuit board through micro-leaks) or simply blows due to age.

When this fuse blows or corrodes, the heater circuit is permanently interrupted. The engine control unit immediately detects the break in the heater circuit, resulting in:

1 The "Urea" / "Engine Management" warning light coming on.

2 A message counting down the kilometres until the engine start is blocked.

3 The heater-related faults being logged in the memory (e.g. P20C2 – heater control, open circuit).

Inserting a 10 kΩ thermistor in place of the thermal fuse and placing it in the duct is extremely dangerous and carries a huge risk of melting the tank or even causing a car fire.

Unfortunately, there are many misleading guides on this subject circulating online, which stem from confusing two different components. Here’s why this solution is a ticking time bomb:

1. Complete confusion of component functions
You are replacing a fuse (emergency cut-off switch) with a measuring component (sensor).

A thermal fuse acts as a protective shield – in the event of a fault, it cuts off the power so that the heater does not heat up indefinitely.

A 10 kΩ thermistor is a resistor whose resistance changes with temperature. It cannot cut off the power. Worse still, if you solder it in series into the heater’s power circuit, it will burn out very quickly, because it is not designed to carry high currents (the heater draws several amps, whereas a small thermistor can only handle fractions of an amp).

2. Why does this risk melting the tank?
The heating mat in the AdBlue tank is very powerful. If the controller (computer) fails and gets stuck in the ‘continuous heating’ mode, the heater will operate non-stop.
Under normal conditions, a thermal fuse would cut the circuit at around 75°C. If you fit a thermistor (or a simple ‘short-circuit’ jumper) in its place, the heater will have no protection whatsoever. The temperature of the plastic inside the tank will quickly exceed 100°C–150°C. The tank’s plastic will start to melt, AdBlue fluid will leak onto the electrical system, leading to a short circuit and a potential fire.

This is about a quarter of what I managed to get out of Gemini

Conclusions: does the power supply to the heater flow through this circuit (yellow cables) and is the thermal fuse part of this circuit? If we bypass it by soldering in a thermistor or another resistor, we are simply bypassing this safety feature and have no protection in the event of a control failure – whether from the AdBlue module or a MOSFET failure – and the heater remains on a constant power supply.

The temperature we see on the diagnostic boxes probably comes from that second thermistor, which is slightly away from the heater itself, and that’s what got me thinking... why would there be two thermistors in the tank? According to AI, the component we’re replacing isn’t a thermistor... And the bimetallic temperature fuse – it doesn’t read the temperature, so it’s no use to us checking it in the DB. Ah, it reads 22°C after soldering in the thermistor... and that it’s OK.
In the event of errors or faults, Diagbox shows 0, but I assume this is simply the result of the entire system being put on hold and does not mean that it was a faulty reading from the ‘thermistor on the heater’ and once, for example, a resistor has been soldered in, the module doesn’t detect the faulty resistance from the damaged fuse, so it assumes everything is OK, and this actual thermistor, located away from the heater, can once again display the correct temperature - does this mean that it is the thermistor we have just soldered in that is showing this, because it has probably only been soldered by us into the heater’s power supply circuit and does not actually perform any measurement functions?

Gemini states that the heater’s power supply is a PWM signal and that in the event of a controller failure or a transistor short-circuit in the module, a constant 12V supply is provided – which, with our heater safety bypass... unfortunately, would result in... THE TANK MELTING AND A POSSIBLE CAR FIRE!!!! /the heater burning out.


So, at the end of the day... if, after this repair, everything else in the AdBlue tank is OK – i.e. the heater control – that’s great, but if the electronics fail, the car could catch fire... and lead to a tragedy.

I had another look at the photo of the heater and it contradicts what Ai suggested, namely that this "temperature fuse" is directly in the heater's power circuit, because I can see in the photo two wires – blue and green – connected to the heater's circuit, and this temperature sensor/ fuse has its own two yellow wires. Now I’m not sure if everything I’ve posted above is just speculation, and what the actual role of this component in the heater is.

IMPORTANT!!
I don’t even know if this information from AI is true... I can see some logic in it, but I’M NOT AN ELECTRONICS EXPERT, so I’d ask more experienced people to comment on this. It would be a bit risky to do without any fire protection in the event of a heater control failure; it’s been on my mind I can’t help thinking that quite a few people take the soldering of the thermistor/resistor as a given, and that it is this component that reads the fluid temperature; but if it is located on the heater, how is it supposed to provide the controller with the actual temperature when the heater is, say, 70°C? And all the more so because, as the thread author mentioned, there is a second thermistor located away from theand reading the AdBlue temperature. I hope I haven’t made a complete fool of myself with this post, but I’m a total amateur – at worst, you’ll just laugh at me .

Added after 2 [hours] 36 [minutes]:

When I asked again, Gemini gave a contradictory answer – I suppose it’s still useless for such purposes – it often gets it wrong and even makes things up.
It stated that yes, it is a thermistor and that soldering the thermistor into this conduit works, and the heater itself is further protected by an algorithm that monitors the maximum continuous operating time of the heater even if the data from this thermistor is incorrect, i.e. the temperature does not rise as quickly as in realitythe heater does not heat up, and the thermistor itself is responsible for three basic functions: protecting the heater from running ‘dry’ and from burning out in the event that air enters the tank or the fluid level is too low, self-diagnostics, whereby supposedly every time the car is started, the system checks all circuits, including firing up the heater for a few seconds, and this thermistor is supposed to detect the change in temperature; otherwise, the system is supposed to determine that the circuit is faulty and trigger urea service errors, etc. (i.e. would a new soldered-in thermistor work reasonably well and register this temperature change in those few seconds?) So soldering in just the resistor itself probably wouldn’t work then, as it wouldn’t pass this initial diagnostic test? And the third function is ‘ice-to-liquid phase control (Local temperature)’ - the controller receives a signal from the thermistor that the ice has already melted locally near the pump and can start the pump, and the heater does not need to run at full load.
I received these two versions , so the previous post may be out of date, but I still don’t really know, whether to believe that this algorithm – even though we are unable to mount this thermistor precisely on the heater without cutting open the tank – if it does indeed temporarily limit the power supply to the heater, then it will protect the tank from the worst-case scenario — such as the tank melting or a fire.