1997 Dodge Ram 1500 P0204 Code: Injector Circuit Open - Diagnosis and Repair Guide

Did you clear the P0204 code, drive the vehicle under normal conditions, and check if it returns? The injector resistance should be approximately 12 ohms ±1.2 ohms at 20°C (68°F). Perform a KOEO test: unplug the injector connector and verify that there is 12 volts on the DG/OR wire. The LT/B wire (also known as LB/BR) should show no voltage and must not be grounded. Also inspect the injector connector and the area about 3 inches from it—this is a common failure zone. Replacement connectors or wiring harnesses are available for this application.

I cleared the code, but it returned immediately. Using a voltmeter, I measured 13.5 volts on both wires at the connector with no interruptions—steady voltage throughout. I performed the 'ear test' using a steel rod and did not hear any clicking from cylinder #4. The other cylinders were clearly clicking. Thanks for the tip, kev2. To clarify: one voltmeter lead was grounded to the vehicle frame during testing. I touched each wire in turn and consistently read 13.5 volts.

A common DIY test is to swap the #4 injector with an injector from another cylinder—this will help determine if the issue lies with the injector or wiring. A noid light makes this test quick and easy. When the injector connector is plugged in, do you have 12 volts on both wires? What about when the connector is unplugged—only one wire should show voltage at that time.

I'm going to need a noid light—I've heard it's available individually. With the engine running and the injector connector disconnected, I measured 13.6 volts on the left wire (viewing down the rail) and only 0.12 volts on the right wire. Also, do you mean swapping the entire injectors or just their connectors?

The standard procedure is to remove the #4 injector and swap it with a cylinder like #1. If the P0204 code shifts to P0201, that indicates a faulty injector. This test can be time-consuming but is effective. I mentioned this because it's a common diagnostic step. Did you perform an ohm resistance check on the injector? When using a noid light—let me know if single units are now available for Dodge models (instead of full kits). For DIYers, one unit should suffice. Also, consider cost versus replacement part value.

I can purchase a standalone noid light online at eBay, Amazon, or even Walmart—around $9 to $15. I rented a set from AutoZone. When I connected it to the injector connector and cranked the engine, there was no response—the light didn’t flash or illuminate. It worked on two other injectors. What should I do now?

This indicates a problem with the #4 injector's driver circuit. The wire from the injector to the Powertrain Control Module (PCM) is likely faulty—or the PCM’s internal driver circuit may be damaged. You already confirmed that when the connector is plugged in, both wires show 12 volts. The DG/OR wire is functioning correctly. The issue lies with the LB/BR wire—the driver wire—which connects to the PCM. Unplug the injector and perform a KOEO test: check this wire using a digital voltmeter (DVOM). Is it grounded? Does it have any voltage? After turning off the key, unplug the PCM’s C2 terminal (white wire), then measure resistance from pin 16 of the injector connector to the wire leading to the PCM. What is your reading?

Okay—assuming I performed this correctly: at KOEO, the left wire reads 12.14 volts, and the right wire reads 0 volts. The ohm readings are 14 ohms on the left wire and 1.7 ohms on the right wire (from pin #16 to connector).

Let’s avoid using 'left' or 'right'—only two wires matter here. The DG/OR wire is the power supply (dark green with orange tracer). The LB/BR wire is the driver circuit (blue wire with brown tracer)—the PCM grounds this to complete the circuit, allowing fuel injection. When the engine is off and the injector is unplugged, check continuity between the LB/BR wire and the PCM terminal #16. What is your ohm reading? Is there a ground connection? How long was the Check Engine Light on with P0204 before you attempted repairs? Did you inspect the wiring at the repair location to ensure no open circuit exists? Diagrams are essential—without them, it's easy to misidentify harnesses or terminals.

My two wires are DG/OR and LG/BR. The ohm reading on the LB/BR wire is 0.00 when the key is off. I likely tested this while removing the fuel rail for a gas leak inspection. When I reassembled everything and started the engine, that’s when the P0204 code appeared. That's why I initially suspected the short between wires might have damaged something.

Yes—this accidental wire contact could have caused a short in the PCM injector driver circuit. These faults often don’t appear immediately but develop over time. During KOEO, with the connector plugged in: both wires should show 12 volts. With the engine running and no noid light response, that suggests the injector is not receiving proper signal. When the injector is unplugged and the PCM is also disconnected, test the LB/BR wire directly between terminals—zero ohms would indicate a failed PCM driver circuit.

It seems like that’s exactly what happened—I didn’t want to replace the entire PCM just yet. But everything points toward a faulty PCM injector driver. That’s disappointing, but I’m grateful for your detailed guidance. Thanks so much—this kind of help is invaluable. It's reassuring to know there are experts out there who understand these systems well.

I hate to condemn PCMs—I’d ask a colleague to weigh in on this before making a final call.

Thanks for the help!

To kev2: After your post, I decided to replace the PCM with model 204.99 at AutoZone. It worked perfectly—no codes, noid light flashed, and the injector operates smoothly. I’m very grateful for your guidance—it pointed me in the right direction. Wish you lived nearby—I’d buy you a beer or three! Thanks again.