Subaru Outback P1469 DPF Fault
Subaru Outback P1469 Fault Code
First things first, a diagnostic scan was carried out using a scan tool. The initial sweep revealed a few issues. There were faults flagged in the ABS system and the parking brake. But the key problem was code P1469, indicating "Limp Home Mode" and a blocked DPF.
What exactly is "Limp Home Mode?" It's a safety feature that restricts engine power when a significant fault is detected. This protects the engine from further damage. It also means a frustratingly sluggish driving experience.
Looking at DPF Live Data
To get a clearer picture, we looked at live data from the DPF. Here's what we checked:
DPF pressure at idle: 60-70 mibars
Estimated DPF soot accumulation: 237%
Kilometres since the last regeneration: 500 km
High DPF pressure at idle is a telltale sign of a blockage. A soot accumulation of 237% confirmed our suspicions.
Common Issues with Asian Diesel Cars
Many Asian diesel cars, including Toyotas, Subarus, and Kias, share similar DPF-related challenges. One common problem is a rising oil level. This happens when diesel fuel gets past the piston rings and contaminates the engine oil.
Why is this a problem? Because these vehicles are designed so that if the oil level rises excessively, the DPF regeneration process will be inhibited. This is a protective measure. It prevents potential engine damage, but it also leads to DPF blockages.
Another crucial factor is the air conditioning (AC) system. On many models, a functioning AC system is essential for passive DPF regeneration. If the AC isn't working correctly, passive regeneration might not occur, contributing to DPF issues.
When the DPF becomes blocked, these cars often display a cascade of warning lights. Skid control, ABS, and parking brake lights might illuminate. Cruise control can also be disabled. Don't be fooled by these seemingly unrelated errors. They often disappear once the DPF fault is resolved.
Getting Ready for DPF Cleaning
With the diagnosis confirmed, we prepared the Outback for DPF cleaning.
First, the engine oil level was checked. Ideally, it should be around halfway between the minimum and maximum marks. It's important to avoid overfilling.
Next, we located the DPF and the DPF pressure sensor. On this Subaru boxer diesel engine, the DPF sits relatively low. The pressure sensor is connected via two tubes.
A manometer was then connected to these tubes to measure the DPF pressure. The smaller tube measures pressure after the DPF, while the larger tube measures pressure before it.
Given that the oil level was a bit high, we extracted some oil using an oil extractor to bring it down to the desired level.
Cleaning the DPF:
The cleaning steps were as follows:
1. A small amount of the cleaner was injected into the DPF and allowed to soak.
2. The engine was started.
3. The remaining fluid was injected into the DPF while the engine was running.
Safety First: It's crucial to run the engine during fluid injection when the DPF is close to the engine. This prevents the fluid from backfilling into the turbo and causing hydrolock. Hydrolock is when liquid enters the cylinders and prevents the pistons from moving, potentially causing serious engine damage.
It's worth noting that Launch UK is currently transitioning to Launch Europe. This transition has led to temporary stock shortages of their cleaning kits.
Monitoring Pressure and Soot
During the cleaning process, we kept a close eye on the DPF pressure. We held the engine revs at around 3,000 RPM. This helps to increase the exhaust gas temperature and promote the breakdown of soot particles.
The goal was to see the DPF pressure decrease. We aimed for a pressure range of 30-40 mibars at idle. However, target pressure ranges can vary between vehicle models. For example, a Transit van might be fine with 8-9 mibars at idle. The same pressure on a Renault Traffic could indicate a failing DPF.
Resetting the DPF and Clearing Codes
After cleaning, it's essential to reset the DPF and clear any stored fault codes.
Using the scan tool, we reset the DPF oil-related learning values. This tells the engine control unit (ECU) that the DPF has been cleaned. An oil change reset was also performed.
Finally, we cleared all fault codes from the ECM and ABS systems. The key was then cycled on and off to ensure all warning lights were extinguished.
The Verdict: A Qualified Success
Initially, the results looked promising. The soot accumulation was reset to zero. The DPF pressure dropped to 10 mibars at idle.
However, the DPF symbol soon reappeared. Further monitoring revealed fluctuating soot accumulation levels during regeneration. This suggested an underlying issue with the DPF itself.
While the cleaning process provided some improvement, the car is ultimately on the borderline of needing a new DPF.