P2156 means the engine computer has detected a lower-than-expected supply voltage on the shared power circuit for Fuel Injector Group D. Because that voltage is needed to energize the injectors, the group may not open or seal properly, leading to drivability problems.
The shared injector feed wire can be chafed, pinched, corroded, or have poor pin contact, causing a voltage drop, short to ground, or open circuit. This is the most common root cause for a supply-voltage-low code.
An injector winding with an internal short or very low resistance can pull the supply circuit down or trigger a low-voltage fault. Testing resistance and comparing injectors helps isolate the offender.
A blown injector fuse, worn relay contacts, corroded splice, or damaged bus bar can reduce or interrupt voltage to the entire injector group.
High resistance in the injector ground path can make the effective supply voltage appear low to the control module and weaken injector operation.
The engine computer can misreport or actually supply low driver voltage, but this is uncommon and should only be considered after wiring, power supply, and injector faults are ruled out.
It is possible but uncommon. Most P2156 faults are caused by wiring, connectors, injector faults, or power-supply problems. The PCM should not be replaced until all of those have been ruled out.
Short trips are usually possible, but misfiring can overheat and damage the catalytic converter. It is best to diagnose and repair the problem promptly.
No. Replace only the injector(s) or repair the circuit that is actually faulty. Proper diagnosis will identify whether the problem is a single injector, the wiring, or the shared power supply.
Group D is a manufacturer-specific grouping of fuel injectors that share a common supply or driver circuit. The exact injectors involved depend on the vehicle design and should be verified with a wiring diagram.