P0403 EGR malfunction after thermostat replacement

[Adv3nture]

This may be an unusual request; I hope someone can provide me with guidance. Wife's Touran, 2.0 TDI CR 140 PS with DSG transmission, CFHC engine code. The signs indicative of a thermostat stuck in the open position were evident, as it took an extended period to reach the desired temperature. No fault codes; operated normally otherwise. Yesterday, I replaced the thermostat, a somewhat unpleasant task. I accessed it from above by detaching the intake manifold and throttle assembly, necessitating the removal of the fuel rail. Initially, things seemed to go well. The vehicle was reassembled successfully; however, during the road test, the coil light began to blink, resulting in the activation of limp mode. Returned to the workshop and connected it, resulting in a P0403 error code. I find it quite dubious that this occurred quickly after significant effort, so I re-examined what I had altered and found nothing amiss. I have disconnected and reconnected all the electrical connections. The vehicle traveled around 15 miles without the warning light activating again. I started and stopped the engine many times over this distance, and all functions operated normally. This dawn, the coil light illuminated once again.

Inquiring about recommendations from others? Is there a connection between the EGR system and the throttle body linked to the intake manifold? The EGR valve seems to be located in the rear of the engine, far from my work area. Upon researching this code, I saw many discussions on the N18 valve. What is its function, and where is it located?

The new thermostat seems to be malfunctioning. The system now reaches temperature more rapidly than before; but, if I reduce the throttle or operate softly for around 30 seconds while the temperature is at mid-range, the coolant temperature decreases somewhat. This indicates that the new thermostat may not be entirely shutting, unless I am overlooking another factor. Does this pertain to the N18?

[Inspirli]

16787 (P0403) - Exhaust Gas Recirculation (EGR) Valve (N18): Failure

The EGR unit is known for its unpredictable failures; the revised component number is 03L 131 512 DQ (genuine VW only; aftermarket parts should not be used).

On Monday, we installed a new driver's seat belt in an A3. Yesterday, the customer returned with the glovebox ajar due to a broken hinge and said that we had damaged it when replacing the seat belt on the other side of the vehicle. This exemplifies the concept of a "rogue customer" that the trade must endure.

Can you envision how you or your spouse would have responded if the task had been completed on your behalf with this result? It occurs sporadically and is disheartening.

[Adv3nture]

Indeed, I am also involved in the trade and fully aware of your activities. To be fair, vehicles may sometimes malfunction unexpectedly during maintenance. I am curious if this EGR defect is related to the recent work I performed, namely the removal of the input manifold and disconnection of components such as the throttle body and N75 valve. While attempting to erase the P0403 code with the engine running, I found that it would not clear. Upon disconnecting the throttle body, the fault status changed from active to passive, and it subsequently cleared. However, disconnecting the throttle body resulted in additional faults that could not be cleared until it was reconnected. The P0403 code did not reappear immediately but returned after several brief trips.

I have heard that aftermarket EGR valves are subpar, and given the cost of authentic VW units, I am inclined to disable the EGR valve and eliminate the related fault codes via mapping. Unless you can provide a compelling rationale against it?

[Inspirli]

Three compelling reasons: I am not an extreme environmentalist, but I assert that everyone is entitled to clean air, particularly those of us with asthma, which we got due to Tony Blair's fixation on diesel fuel.

Furthermore, it is unlawful.

[Adv3nture]

Acknowledged.

My inclination is to rectify issues thoroughly, which is the reason for my post here. I appreciate that these engines often function well and run admirably without modifications; I would not consider a performance remap, since this is my wife's everyday vehicle. I am uncertain if my work has caused this issue or whether it has coincidentally occurred simultaneously and only requires an EGR valve, as indicated by the problem code.

To what extent are you familiar with these engines? Could a fault code, such as the one I am receiving, be activated by a poor connection related to any components I have altered? (for instance, the throttle body). What caused the error to remain unresolved but go inactive when disconnecting the throttle body? The throttle body seemed not to operate as a shutdown flap when the engine was turned off with the error code present. It would come to a jarring halt rather than ceasing operation smoothly. The vehicle is now operating well. The glow plug indicator illuminated again yesterday upon her return home; however, when she drove later, the car functioned well and covered around 15 miles without any problems.

Does the existence of an EGR fault code, whether active or stored, influence the initiation of a DPF regeneration? The DPF is intact and seems to function well, as there is consistently no soot on the rear of the vehicle, and the fuel efficiency remains between 40-45 mpg, which is satisfactory for a Touran DSG mostly used for local B-road travel.

[Adv3nture]

It is not the N75 solenoid; rather, it pertains to the solenoid associated with EGR cooling flow regulation. I recall that disconnecting and reconnecting it resulted in the generation of EGR error codes.

[Bedelon]

Manipulating emissions is unacceptable here...

[Adv3nture]

It is rather ironic, really. Disregard my previous remark.Rolling on the floor laughing my ass off:

[Adv3nture]

Is it feasible to purchase only the actuator? I am capable of disassembling and cleaning the EGR valve and purging the cooler core. I am unable to locate one anywhere. TPS is charging £422 including VAT for the whole assembly.