Quote Originally Posted by Anthony k View Post
Codes as follows
PO172
PO117
PO175
PO421
PO431
Sounds like you have more than one issue. Fuel pressure bleeding down would be the fuel pump check valve in the pump or leaky injectors. Since you are running rich, this may point more to leaky injectors. Below is all the info on your codes:

PO172
16556/P0172 - System Too Rich, Bank 1

Possible Symptoms
• Irregular behavior

Possible Causes
• Fuel system
• Excessive fuel pressure
• Leaking or contaminated fuel injectors
• Leaking fuel pressure regulator
• Low fuel pressure or running out of fuel
• Vapor recovery system
• Air leaks after the MAF
• Vacuum leaks
• Improper seated engine oil dipstick
• Stuck EGR valve
• Oil overfill
• Cam timing
• Cylinder compression
• Exhaust leaks before or near HO2Ss.

PO117
16501/P0117 - Engine Coolant Temperature Sensor (G62): Signal too Low

Possible Symptoms
• Difficulties with starting a cold engine.
• Starting the engine when engine is warmish or warm, idle rpm immediately is 1200 - 3000 rpm.
• RPM at idle is irregular.
• With all engine temperatures seldom idle rpm will vary between 900 - 1000 rpm.
• With engine warm (90 °C) the engine temperature suddenly drops (70 °C) and slowly comes back to 90 °C.
• Bad acceleration during warming up.
• Diesel: an indication is extreme long time burning time of the glow indication light.
• Engine Overheating

Possible Causes
• The electrical signal coming from G62 is too low
• Wiring and/or connections faulty (short circuit?)
• Engine Coolant Temperature Sensor (G62) faulty
• Mechanical problems in cooling system

Possible Solutions
• Check wiring and connections
• Check / Replace Engine Coolant Temperature Sensor (G62)
• Check cooling system and correct overheating condition if present
Special Notes*
• In MY 1995-2002 (?) in Europe at VW-cars the G2/G62 had the bad reputation of breaking down often. The default G2/G62 is black and all replacements are green.

PO175
16555/P0171 - System Too Rich, Bank 2

Possible Symptoms
• Irregular behavior

Possible Causes
• Fuel system
• Excessive fuel pressure
• Leaking or contaminated fuel injectors
• Leaking fuel pressure regulator
• Low fuel pressure or running out of fuel
• Vapor recovery system
• Air leaks after the MAF
• Vacuum leaks
• Improper seated engine oil dipstick
• Stuck EGR valve
• Oil overfill
• Cam timing
• Cylinder compression
• Exhaust leaks before or near HO2Ss.

PO421
16805/P0421/001057 - Warm Up Catalyst; Bank 1: Efficiency Below Threshold

Possible Causes
• Warm Up Catalyst Bank 1 faulty

Possible Solutions
• Check Warm Up Catalyst Bank 1
• Set Readiness
• Replace Warm Up Catalyst Bank 1
Special Notes*
• When found on the following, there may be a firmware update:
• 2000 - 2001 Passat with ATQ engine, see TSB 01-07-07 (TPI 2010372)
• 2000 - 2001 A4 or A6 with ATQ engine, see TSB 26-08-07 (TPI 2013086)
• 2001 Allroad with APB engine, see TSB 01-08-20 (TPI 2005579)
• 2001 A4 or A6 with APB engine, see TSB 01-08-34 (TPI 2012357)

PO431
16815/P0431/001073 - Warm Up Catalyst; Bank 2: Efficiency Below Threshold

Possible Causes
• Warm Up Catalyst Bank 2 faulty

Possible Solutions
• Check Warm Up Catalyst Bank 2
• Set Readiness
• Replace Warm Up Catalyst Bank 2
Special Notes*
• When found on the following, there may be a firmware update:
• 2000 - 2001 Passat with ATQ engine, see TSB 01-07-07 (TPI 2010372)
• 2000 - 2001 A4 or A6 with ATQ engine, see TSB 26-08-07 (TPI 2013086)
• 2001 Allroad with APB engine, see TSB 01-08-20 (TPI 2005579)
• 2001 A4 or A6 with APB engine, see TSB 01-08-34 (TPI 2012357)

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