| P1641 – Fuel Pump Primary Circuit Failure (Ford)
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Manufacturer Specific Definitions for P1641
Table of Contents
- What Does Code P1641 Mean?
- What are the common causes of code P1641?
- What are the symptoms of code P1641?
- How do you troubleshoot code P1641?
- Codes Related to P1641
- Get Help with P1641
What Does Code P1641 Mean?
OBD II fault code P1641 is a manufacturer-specific code that some manufacturers define as “Fuel Pump Primary Circuit Failure”, and on applications that use this definition, the code is set when the PCM (Powertrain Control Module) detects a failure of the electrical circuit that controls the fuel pump on gasoline engines. Refer to the “Related Codes” section of this guide for other definitions of code P1641.
In a functional system, the fuel pump is activated for a second or two when the key is turned to the “ON” position to prime and pressurize the fuel system. If the engine does not start, or the key is left in the “ON” position, the PCM will deactivate the fuel pump after a period of time set by the manufacturer. To keep the fuel pump activated (running), the PCM needs to see signals from several sensors that the engine has actually started, and that it is running normally. In this regard, the most important signal is from the engine speed sensor that transmits the engine RPM to the PCM.
In practical terms, when the ignition circuit is activated, a dedicated relay is energized to supply power to the fuel pump. The advantage of a relay is that a low amperage circuit is used to close a high amperage circuit by means of energizing an electro-magnet, which in turn, pulls a moveable contact point into contact with a stationary live contact point. This means that the delicate electronics in the PCM does not have to supply high-amperage current to an electrical consumer, which in this case, is the fuel pump.
However, long use can cause the contact points of the high amperage switch in the relay to “burn” away to the point where contact is no longer possible. When this happens, the circuit is seen by the PCM to have failed, and code P1641 will be set as a result.
The image below shows the construction of a typical fuel pump relay. Note that while the basic construction and working of fuel pump relays are much the same across all manufacturers, the actual appearance, location, and number of pins on the relay vary greatly between applications. Always consult the manual for the application being worked on to determine the location of the fuel pump relay. Note the normally open contact points in the top right hand corner of the image- these are the contacts that are “pulled” closed when the relay is energized, thereby supplying power to the electrical consumer.
What are the common causes of code P1641?
The most common cause of code P1614 is failure of the fuel pump relay. Other possible causes could include the following-
- Damaged, burnt, shorted, or corroded wiring and/or connectors
- Open circuits
- Defective fuel pump resistors (where fitted)
- Defective or failed fuel pump motor
- Defective fuel pump control module
- Failed, or failing PCM. Note that this is a rare event, and the fault must be sought elsewhere before any controller is replaced.
What are the symptoms of code P1641?
Apart from a stored trouble code and an illuminated warning light, the main symptom of this code is that the engine won’t start because the fuel pump cannot be activated. Other possible symptoms could include the following-
- Non-start conditions may be erratic in the case of intermittent failures of the relay and/or control circuit.
- Engine may stall or shut off unexpectedly in cases where intermittent faults are present.
- In cases where the relay contact points have fused together, the fuel pump may run continuously while the ignition is “ON”.
How do you troubleshoot code P1641?
NOTE #1: On some applications, the fuel pump relay works in conjunction with a resistor to reduce the current to the fuel pump. In most cases where a resistor is present, the current is reduced to 9 volts, but always consult the manual for the application being worked on to determine the correct working current for the fuel pump on that application.
NOTE #2: On some applications, the fuel pump is controlled by a dedicated control module, most notably on some VAG products. On these applications, the module is known to be problematic, and it should therefore be the first item to be checked during a diagnostic procedure for this issue.
NOTE #3: On other applications that use dedicated fuel pump control modules, the diagnostic and repair procedures are make-and-model specific. Consult the relevant repair manual for these applications for accurate diagnostic and repair information.
Record all codes present, as well as all available freeze frame data. This information can be useful should an intermittent fault be diagnosed later on.
NOTE: Check the battery condition and state of charge at this point to ensure that full system current is available to the fuel pump control circuit.
If the scanner has control functions, command the fuel pump on and off multiple times to see if an intermittent fault is present. If the pump does not activate, consult the manual to locate the fuel pump relay.
Inspect the pump relay for signs of damage or overheating, which could indicate poor connections on the relay pins, or an excessive current draw. Note however that in many cases, a relay will show no outward signs that it has failed.
With the relay removed, prepare to test the circuit by bridging the relevant contact points in the fuse box.
WARNING: Bridging the correct contact points is relatively easy if the relay has only four pins, but on relays with five, or even six pins, identifying the fuel pump circuit can be a tricky. One way to avoid potentially expensive mistakes is to use a relay by-pass, an example of which can be seen in the image below.
The toggle switch is designed to isolate a circuit. Therefore, by replacing the regular relay with a bypass for testing purposes, the fuel pump can be activated (and deactivated) simply by toggling the switch. Thus, if the pump activates with the bypass in the “ON” position, the regular relay is defective, and must be replaced.
NOTE: Relay bypasses are available in various configurations to fit most applications, and are available for a few dollars at most auto parts stores, or online. Using such a device eliminates the possibility of bridging the wrong pins or terminals in the fuse box, and their use is therefore highly recommended.
If bridging the correct terminals in the fuse box, or using a relay bypass does not activate the fuel pump, consult the manual on whether the application is fitted with a fuel pump resistor. If such a resistor is fitted, locate it and test its resistance according to the procedure stated in the manual. Compare the obtained reading with the stated value, and replace the resistor if the obtained value does not agree with specifications.
If the fuel pump still fails to activate despite the relay and resistor (where fitted) are fully functional, prepare to perform a visual inspection of all associated wiring and connectors. Consult the manual to determine the location, function, routing, and color-coding of all wiring, and look for damaged, burnt, disconnected, shorted, or corroded wiring and/or connectors. Make repairs as required, clear all codes, and attempt to activate the fuel pump again.
NOTE#1: If the pump activates after repairs to wiring are complete, consult the manual on the recommended amperage draw for this circuit. If the engine starts, monitor the amperage draw in the circuit with a multimeter or the scanner, but note that the displayed reading should remain constant, and within stated specifications.
NOTE #2: Gasoline fuel pumps deliver fuel at a constant rate and pressure; therefore, the current they draw should also be constant. Fluctuations in the current drawn indicate a failing pump motor, while an excessive current draw could indicate obstructions in the fuel system such as clogged or dirty fuel filters, clogged/damaged fuel lines, or even defective fuel pressure regulators. Note however that where an excessive current draw is present, other fuel system or electrical related codes are likely to be present as well.
If no visible damage to wiring is found, and the fuel pump relay and resistor (where fitted) are in working order, prepare to perform input voltage, ground, resistance, and continuity checks on all associated wiring and connectors. Bear in mind that the fuel pump motor forms part of the control circuit and as such, its resistance must be tested as well. Be sure to disconnect the circuit from the PCM during resistance/continuity checks to avoid damage to the controller.
Compare all obtained readings with the values stated in the manual, and make repairs as required if discrepancies and/or deviations are found. Note that in some cases, it may be necessary to remove the fuel pump from the tank to make it easier to test the pump motor.
NOTE: Be sure to test the system wiring between the ignition switch and the fuel pump relay as well. Defective ignition switches can interrupt the power supply to various other components (including the fuel pump relay), so pay particular attention to the ignition switch itself, as well as other connections between the ignition switch and the fuel pump relay for evidence of intermittent, or sporadic faults.
Clear all codes after repairs are complete, and activate the fuel pump to verify that repairs had been successful. Operate the vehicle for at least one complete drive cycle with the scanner connected to monitor the working of the fuel pump in particular, and the fuel system in general.
If symptoms persist, or return after the completion of several drive cycles, it is likely that there is an intermittent fault present. Note that some intermittent faults can be extremely challenging to find and repair and in some cases, it may be necessary to allow the fault to worsen before an accurate diagnosis and definitive repair can be made.
Codes Related to P1641
- P1642 – Relates to “Fuel Pump Monitor Circuit High Input”
- P1643 – Relates to “Fuel Pump Monitor Circuit Low Input”
- P1644 – Relates “Fuel Pump Speed Control Circuit Malfunction”
- P1645 – Relates to “Fuel Pump Resistor Switch Circuit Malfunction”
NOTE: Depending on the application, the related codes listed above may have other definitions. Also note that some manufacturers have assigned definitions to code P1641 that do not relate to the fuel pump control circuit at all, except in the case of Saab, who have assigned oxygen sensor related faults to this code in addition to fuel pump control circuit problems. Below are some other examples of different definitions of code P1641-
- Chrysler/Dodge/Jeep – Cabin Heater 1
- Daewoo – VI MOTOR COIL 2 OPEN/SHORT
- GM – Malfunction Indicator Lamp (MIL) Control Circuit
- Honda – ACTTRQ Motor Torque Signal Circuit High Input
- Saab – Fuel Pump Relay- No Voltage to fuel Pump and O2S Preheating.
- Saturn – Quad Drive A Quick Set Detected A Fault
- Volkswagen/Audi/Volvo – Please check DTC Memory of Air Condition ECU
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