No. 2129.1

Bulletin #: 2129.1
Advanced Technical Information
Part ID: 2003
2
971 – Fuel Delivery and Suspected Fuel Vapor Lock
Vehicles Affected
Models
Model Year
Model Type
VIN Range
Vehicle-Specific Equipment
Panamera
As of 2017
971
N/A
N/A
Revision History
Revision
Release Date
Changes
0
November 29, 2021
Original document
1
February 22, 2022
Fault Tree revisions
Condition
Customer complains of a check engine light resulting from faults in the DME (e.g. DME V8 TFSI (ULEV/C6B)) for:
P008700_ Fault 000B16 “Fuel high-pressure system, pressure – below limit value”
and/or
P01C800_ Fault 00403E “Fuel high-pressure system, bank 2, pressure – below limit value” accompanied by
misfires, stalling and or a rough idling engine.
Technical Background
Controlled spark ignition over a wide-range of operating conditions (e.g. temperatures, altitudes) necessitates the
altering of a fuel’s volatility, or its vapor-forming characteristic as a function of temperature. Emissions reduction
is also an optimization parameter considered for fuel formulation. The standard imposed by the Environmental
Protection Agency to establish volatility tolerancing, establishes limits based on geographic region and calendar
month. Design requirements for fuel delivery systems allow for such in fuel volatility; nonetheless, large deviations
from allowed tolerances can cause delivery and injection issues resulting from a condition referred to as vapor lock.
Vapor lock, characterized here as the premature vaporization of fuel in the delivery system prior to combustion, can
cause the symptoms described in the ‘Condition’ section above. During colder months in colder regions, fuel
volatility (vapor pressure) will be higher as compared against months where the average temperature is warmer.
If this volatility exceeds established tolerances, especially at higher ambient temperatures and or higher altitudes,
vapor lock can result, causing a loss of fuel pressure, thereby disrupting delivery.
However, it is important to first diagnose and rule out other causes before deeming vapor lock the suspected culprit.
AfterSales
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Bulletin #: 2129.1
Advanced Technical Information
Part ID: 2003
2
Service Information
In an ideal diagnostic scenario, complaints for G2 vehicles consistent with the information provided above will be
reproducible; and the same gasoline will be in the fuel tank as when the initial error experienced by the customer
occurred. To reproduce suspected vapor lock, the engine should be idling at operating temperature, standing safely
in an area that is warmer and without wind to avoid convection cooling of the radiator and other thermal
components. The vehicle may need to idle for 15 min or more at operating temperature to develop possible vapor
lock. If the issue is reproducible, logging actual values with PIWIS Tester is useful to check both the low-pressure
and high-pressure delivery circuits for possible causes before proceeding into diagnosis.
Figure 1 - Fuel Pressure Operation at Idle of a G2.I Configured with V8
Actual: Low-pressure fuel (≈ 5.5 – 6.5 bar)
Set point: Low-pressure fuel (6 – 6.5 bar)
Actual: High-pressure fuel bank ( ≈ 70 bar at idle)
Set point: high-pressure fuel bank 2 ( ≈ 70 bar at idle)
Figure 1 cites an example of properly functioning high and low pressure fuel circuits. The signals in Figure 1 illustrate
the behavior of the low-pressure circuit as controlled by the DME when significant drops in high-pressure occur.
(This specific function only exists in V8 equipped order types.) Specifically, we see the step-change in the lowpressure set point from 6 to 6.5 bar (green) to better supply the high-pressure circuit. The result in this instance is
a correction to both the low- and high-pressure fuel systems, as witnessed by their respective actual values. In
instances of extreme fuel volatility, vapor lock can otherwise result (see Figure 2). The design countermeasure
exhibited in Figure 1 can be helpful in most cases, but might not remedy all highly volatile situations. It is important
to first diagnose the high- and low-pressure circuits individually, starting with the low-pressure side, to rule out any
physical issues with the systems (e.g. a blockage and/or a faulty fuel pump).
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Bulletin #: 2129.1
Advanced Technical Information
Part ID: 2003
2
Figure 2 - Significant High Pressure Deviations, Banks 1 and 2
In contrast to Figure 1, the example in Figure 2 suggests the low-pressure fuel supply is functioning properly, but
both high-pressure supplies for banks 1 and 2 are not.
If both the high- and low-pressure fuel delivery systems function as intended when trying to replicate the issue,
but do not alleviate the concern, then please log the behavior of the system consistent with the signals and method
used in Figure 1 (i.e. four fuel channels displayed in one graph). If the fuel quality is suspect, please collect a sample
from the fuel in the vehicle for testing in accordance with ATI 2130. Please remove the suspect fuel from the tank
and refill with fuel from a known, trusted and reliable source. Alternatively, refill from a pump or gas station used
regularly by the business in its service and repair of Porsche vehicles. Afterward, please repeat the same diagnostic
test used to replicate the suspected vapor lock, ensuring the issue is resolved. If the issue is not resolved, please also
collect a fuel sample from the known, ‘good’ source per ATI 2130. From this point, follow the rest of the procedure
outlined in Figure 3 below.
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Bulletin #: 2129.1
Advanced Technical Information
Part ID: 2003
2
Figure 3 - Fault Tree for Diagnosing Suspected Vapor Lock
Upon arriving at ‘Steps (4) and (5)’ of Figure 2 please consult ATI 2130.
Warranty
As always, please document the repair completely in PQIS.
For this repair, please code the “cause” as follows:
Cause location:
20030 Fuel
Cause symptom:
5061 pressure too low
Use the following troubleshooting labor operation:
20029599		
Checking low- and high-pressure fuel systems (100 TU)
20031750		
Fuel drain and fill (78 TU)
Search Items
Vapor lock, vaporization, low-pressure fuel system, high-pressure fuel system, P008700_000B16 “Fuel highpressure system, pressure – below limit value” and/or P01C800_00403E “Fuel high-pressure system, bank 2,
pressure – below limit value”, vapor pressure, winter fuel blend
Important Notice: Technical Bulletins issued by Porsche Cars North America, Inc. are intended only for use by professional automotive technicians who have attended Porsche service training courses. They are
written to inform those technicians of conditions that may occur on some Porsche vehicles, or to provide information that could assist in the proper servicing of a vehicle. Porsche special tools may be necessary in
order to perform certain operations identified in these bulletins. Use of tools and procedures other than those Porsche recommends in these bulletins may be detrimental to the safe operation of your vehicle, and
may endanger the people working on it. Properly trained Porsche technicians have the equipment, tools, safety instructions, and know-how to do the job properly and safely. Part numbers listed in these bulletins
are for reference only. The work procedures updated electronically in the Porsche PIWIS diagnostic and testing device take precedence and, in the event of a discrepancy, the work procedures in the PIWIS Tester
are the ones that must be followed.
A11625
©2022 Porsche Cars North America, Inc.
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December 22, 2022
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