What does it mean?
This is a generic powertrain diagnostic trouble code (DTC) that applies to many OBD-II vehicles (1996-newer). This may include, but is not limited to, vehicles from Ford, Dodge, Toyota, Chrysler, Jeep, Ram, Chevrolet, Nissan, Mitsubishi, Mercedes, etc. Although generic, the exact repair steps may vary depending on the year, make, model, and powertrain configuration.
If the P0629 code appears, it means a problem has been found in the fuel pump control circuit “A”. More specifically, it means that a voltage situation higher than normal has been detected. Typically, it is caused by damaged wires/connectors in the circuit or the CAN (Controller Area Network) bus. The Powertrain Control Module (PCM) or Engine Control Module (ECM) normally identifies this code, but other support modules may also trigger this particular code, such as:
Alternative Fuel Control Module
Fuel Injection Control Module
Turbo Control Module
Depending on the vehicle’s make and model, it may take several drive cycles before this code can be activated, or it may also be an immediate reaction as soon as the ECM recognizes the fault.
The fuel pump is an integral part of the vehicle’s overall operation. After all, without the fuel pump, no fuel would be delivered to the engine. The control circuit is generally responsible for turning the pump on and off based on the operator’s needs. An open in said circuit could also result in the P0629 code being triggered, so be aware of that before proceeding with any type of diagnosis.
A typical fuel pump:
P0629 Fuel Pump
Fuel Pump Control Circuit A codes include:
P0627 Fuel Pump Control Circuit “A” / Open
P0628 Fuel Pump Control Circuit “A” Low
P0629 Fuel Pump Control Circuit “A” High
P062A Fuel Pump Control Circuit “A” Range/Performance
How severe is this DTC?
This particular fault code is a moderately serious problem for your vehicle. You can still use your vehicle despite the issue. However, it is highly discouraged to do so, as you risk intermittently supplying fuel to the engine, and an erratic or fluctuating fuel mixture could definitely lead to serious engine damage.
What are some of the symptoms of the code?
Symptoms of a P0629 fault code may include:
Check Engine Light is on
Engine does not start
Engine misfires/stalling
Engine starts but dies
Fuel economy is reduced
Engine cranks but does not start
Engine dies when reaching operating temperature
Note: It is always possible that the problem is not resolved, even if the Check Engine Light does not come on immediately. Always ensure your vehicle has undergone a few drive cycles, i.e., drive the car for a week; if the CEL (Check Engine Light) is not on by the end, the problem is most likely resolved.
What are some of the common causes of the code?
Causes
of this code may include:
Problems with the fuel pump itself
Cut or damaged ground wire in the device control module
Unsecured ground strap in the control module
Open, shorted, or corroded wiring in the CAN bus
A faulty CAN bus
Unsecured harness and wires causing chafing or a broken circuit
High resistance in the circuit (e.g., melted/corroded connectors, internal wire corrosion)
What are the P0629 troubleshooting steps?
The first thing I recommend you do is look for Technical Service Bulletins (TSBs) for the specific vehicle by year, model, and powertrain. In some circumstances, this can save you a lot of time in the long run by pointing you in the right direction.
Basic Step 1
You should always immediately scan and test each module using an OBD-II scanner to get a good idea of the general electrical state of your vehicle and its modules. You should also always perform a visual inspection of the connectors and wiring, in case something is obviously damaged, in which case it should be repaired or replaced. Often, these are located under the vehicle near the fuel tank. They are sensitive to road debris and the elements, so pay close attention to their condition.
Basic Step 2
When dealing with a component with its own module (e.g., fuel pump module, etc.), you should examine the ground circuits. You can do this using a separate battery ground. Sometimes you can do this easily using an auxiliary ground cable. If your problem is resolved with the auxiliary ground attached but returns when the OEM ground is used, it means your ground cable is the source of the problem and needs to be repaired or replaced. Grounds should always be carefully inspected for corroded connections, terminals, pins, etc., that could cause circuit resistance. A good sign of excessive corrosion is a green ring around the connector attached to the battery’s positive terminal. If this is present, remove the terminal and clean all contact points, the connector face, and the terminal/stud.
Basic Step 3
Since the cause of the P0629 code could be an open circuit, you need to identify the circuit using an electrical wiring diagram found in your service manual. Once identified, you can individually trace the fuel pump control circuit A wire to see if there are any obvious breaks in the wire. Repair if necessary by soldering the wire (which I recommend) or using butt connectors with heat shrink to insulate it from the elements. Using your multimeter, you can measure the resistance between the circuit connectors to locate the short/open location. A power probe-type tool is highly recommended here in case of a fault somewhere within the entire circuit.
I hope this article has been helpful in guiding you in the right direction to diagnose the problem with your fuel pump control circuit fault code. This article is strictly informational, and the specific technical data and service bulletins for your vehicle should always take priority.