FAQ
TL;DR: 99% of cases trace the -18°C AdBlue reading to a spoofing resistor on the 4‑pin tank harness—“the resistor is connected to the cable exiting the adblue tank.” [Elektroda, decard86, post #16738714]
Why it matters: If DMCI/EAS shows no faults, you may be chasing a programmed-out SCR system rather than a simple sensor issue. This FAQ helps owners and technicians restore a 2008 DAF XF105 AdBlue system that reads −18°C and hides errors.
Quick Facts
- Temperature sensor check point: measure resistance on AdBlue module pins 18–19 to verify tank sensor integrity. [Elektroda, mariomalinie, post #16733857]
- Tank connector uses 4 pins: two for level, two for temperature; spoof resistor often sits on this harness. [Elektroda, decard86, post #16738714]
- A constant −18°C reading typically indicates a fixed resistor mimicking a frozen tank sensor. [Elektroda, kisiol, post #16728945]
- Zero errors with NOx sensors unplugged suggests emulator use or SCR fault tables removed in software. [Elektroda, MobilTruck, post #16831044]
- “Hidden emulator or reprogrammed DMCI” is a common root cause when diagnostics look clean. [Elektroda, stanisławpiotr, post #16733410]
Why does my DAF XF105 show −18°C AdBlue temperature?
A constant −18°C usually points to a spoofed tank temperature signal. Owners often find a fixed resistor wired into the 4‑pin tank connector harness, making the ECU think the fluid is frozen. This disables dosing without logging normal sensor faults. Inspect the tank harness carefully for added components or non‑OEM joints. “It’s definitely about the tank,” so start at the tank-side connector. [Elektroda, stanisławpiotr, post #16732242]
Where is the spoof resistor typically installed?
Technicians report the resistor is most often placed on the cable exiting the AdBlue tank at the 4‑pin connector. Two pins carry level and two carry temperature; the spoof bridges the temperature pair. If present, you may see heat‑shrink, tape, or non‑factory splices near this plug. “At 99%, the resistor is connected to the cable exiting the adblue tank.” [Elektroda, decard86, post #16738714]
Which pins carry the AdBlue temperature signal on the module?
Measure the temperature sensor across pins 18 and 19 on the AdBlue module connector. Compare the resistance you read to the expected values for ambient temperature. A fixed, out‑of‑range value indicates a spoof or failed sensor. Quote: “Check the resistance between pins 18 and 19 of the adblue module.” [Elektroda, mariomalinie, post #16733857]
How do I test for a tank-sensor spoof in three steps?
- Unplug the 4‑pin AdBlue tank connector and visually inspect for added resistors or splices.
- At the AdBlue module, measure resistance between pins 18–19 with a multimeter.
- If resistance does not track ambient temperature, remove any inline resistor and recheck values. [Elektroda, mariomalinie, post #16733857]
Why do DMCI/EAS show zero errors even with NOx sensors disconnected?
If NOx sensors are unplugged yet no faults appear, the system may run with an emulator or modified firmware that suppresses error tables. This masks diagnostic trouble codes and keeps the dash largely clear while SCR is inactive. It explains why removing the AdBlue fuse may only light the exhaust warning. [Elektroda, mariomalinie, post #16733817]
Does a 2008 DAF XF105 always have factory NOx sensors?
No. Some 2008 models did not ship with factory NOx sensors. A missing NOx sensor does not always mean tampering, though paired with zero faults it raises suspicion of further modifications. “It seems to me that your car model did not have factory noxes.” [Elektroda, decard86, post #16738714]
How can I restore DMCI so it ‘sees’ AdBlue again?
First, physically restore the hardware: remove any spoof resistor, reconnect NOx sensors if equipped, and fix wiring. If diagnostics still show no SCR faults, the ECU may be reflashed to ignore errors. In that case, revert the flash to stock using dealer tools or a known‑good file. [Elektroda, MobilTruck, post #16831044]
What is DMCI on the DAF XF105?
In this thread, DMCI refers to the engine management controller that coordinates with the EAS (AdBlue/SCR) module. If DMCI is reprogrammed to suppress SCR faults, standard diagnostics can show no errors despite hardware removal. [Elektroda, stanisławpiotr, post #16733410]
What is the AdBlue/EAS module?
The EAS is the selective catalytic reduction controller that reads tank level and temperature, manages the pump, and doses urea. It interfaces to the tank via a 4‑pin connector and reports faults to the engine ECU (DMCI) over the vehicle network. [Elektroda, decard86, post #16738714]
Can ESA reprogramming alone fix a programmed‑out SCR system?
If someone removed fault tables in the flash, you must reflash with original content. Routine parameter programming with ESA will not restore deleted diagnostic logic. Ask for a stock file and compare checksums before writing it back to the module. [Elektroda, MobilTruck, post #16831044]
What symptoms point to a hidden emulator vs. a simple resistor?
A simple resistor typically locks the tank temperature near −18°C and may still allow some faults. An emulator or modified firmware suppresses multiple errors at once, even with NOx sensors unplugged or the AdBlue fuse removed. Zero errors with missing sensors suggests deeper changes. [Elektroda, stanisławpiotr, post #16733410]
What does removing the AdBlue fuse actually do on this truck?
In the reported case, pulling the AdBlue fuse triggered the exhaust warning lamp, yet EAS logged no faults and DMCI reported no problems. That behavior aligns with an emulator or altered diagnostics rather than a healthy SCR system. [Elektroda, kisiol, post #16728945]
How many pins are on the DAF XF105 AdBlue tank connector, and what do they do?
There are four pins: two for fluid level and two for temperature sensing. A spoof resistor usually targets the temperature pair. This 4‑pin detail helps you separate wiring faults from intentional bypasses during inspection. [Elektroda, decard86, post #16738714]
Could my truck be fully functional yet show −18°C?
Yes, the drivetrain can run seemingly fine with dosing disabled if the temperature input is fixed. However, the SCR system is not working, and emissions control is compromised. The constant −18°C reading is your clue to investigate the tank sensor circuit. [Elektroda, kisiol, post #16728945]
What’s an edge case to watch for when chasing the −18°C fault?
Some 2008 units lacked factory NOx sensors. If your diagnostics show zero NOx entries, verify via VIN before assuming removal. If they truly are absent yet faults stay suppressed elsewhere, expect additional wiring or software tampering. [Elektroda, decard86, post #16738714]
Where should I start if no emulator is visibly present?
Perform a meticulous harness inspection, then resistance‑test pins 18–19 at the module. If values look normal and faults remain absent despite unplugging sensors, suspect a software modification and plan for a stock reflash. [Elektroda, mariomalinie, post #16733857]
