2

Bulletin #: 2129

Advanced Technical Information

Part ID: 2003

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

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.

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Bulletin #: 2129

Advanced Technical Information

Part ID: 2003

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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 support 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 with tester is useful to check both the low-pressure and high-pressure
delivery circuits for possible causes before proceeding into diagnosis.

Increase in Low Pressure Set point (green) as a response to a
pressure reduction seen in the high-pressure system

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)
The plot in Figure 1 illustrates the behavior of the low-pressure circuit as controlled by the DME when significant
drops in high-pressure occur (this specific function exists in V8 equipped order types). Specifically, we see the
step-change in the low-pressure 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, but my not remedy all, highly volatile situations.
Figure 1 cites an example of properly functioning high and low pressure fuel circuits. 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

Advanced Technical Information

Part ID: 2003

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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, from a pump or gas station used regularly
by the business in its service and repair of Porsche vehicles. Please repeat the same diagnostic test used to
replicate the suspected vapor lock, ensuring the issue is resolved. Please also collect a fuel sample from the known,
‘good’ source per ATI 2130.

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Bulletin #: 2129

Advanced Technical Information

Part ID: 2003

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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
©2021 Porsche Cars North America, Inc.

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