The Following Jeep Technical Write-Up Details the Diagnosis and Repair Process of a P0201 fault on a 2000 Jeep Cherokee XJ. This model follows the part number for a 2000 Automatic Federal Emissions. Electrical work, especially that relating to the powertrain control module, should not be attempted by those inexperienced in such fields. This repair was done with the help of a longtime electrical and computer engineer who has worked on circuit boards for decades.
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Code P0201 relates to the OBD fault code "Fuel Injector #1 circuit malfunction". P0202, P0203, P0204, P0205, P0206 would follow for the same computer reading on injectors #2-6, respectively. The first method to understand this fault is to first look into the electrical control that goes into the fuel injection process on most modern vehicles, including this Jeep specific repair.
A constant positive (+) supply of power is provided to the injector splice (OR/GR) by the ASD (Auto Shutdown) relay. This relay works in depth with the control system and computer, but in short provides this power within seconds of the ignition being switched to on, or the vehicle starting and continuing to run. The first test is to determine the supply of positive current. On many Jeep vehicles, all 6 injectors are spliced from an Orange/Green wire. This goes to one of the two terminals of the fuel injector connector. Pull out your multimeter. Take a volt reading, it should supply upwards of 12V. In my testing the 2000 XJ provided 14v to each injector #1-6. The injectors are all receiving power, great! Now to find the real issue that causes the lack of injector pulse.
The injector firing works in a pulse like manner. In order to achieve a proper ratio of fuel to air, the computer monitors other sensors including the timing of the CPS, with the status of the fuel system. In short, the computer repeatedly grounds and un-grounds the circuit to each injector at intermittent timing.
The next test to determine a lack of pulse is easy, cheap, and convenient. The noid light test provides a visual examination of injector pulse. Noid Lights can be purchased in a kit here or easily rented at an auto parts stores. I picked up a rental from O'reilly Auto Parts and confirmed what the P0201 and rough idle was already telling me. No pulse illumination on injector #1. All other injectors passed the test fine.
In my case, all injectors were recently replaced as part of an engine swap and fuel system overhaul. These are the replacement XJ injectors I purchased. New parts don't always mean good parts, but the resistance of the #1 was equal to that of the others, and switching between #1 and #2 still had an issue on #1 and not a P0202 as a bad injector would tend to cause. The noid light test tells you that the circuit is either never being closed (light never turns on) or is stuck open and dumping a constant stream of gas into the cylinder (light remains on, no flicker).
At this point, it is known that the positive (+) part of the circuit is functioning. The negative is now the issue. In a circuit stuck open this likely signals a break in the ground wire from the injector to the PCM, or an internal issue in the PCM, as was my case. After disconnecting the battery, pull the middle PCM plug (relevant to 2000 Jeep vehicles) and using a wire diagram (I use this Haynes book) determine which wire is the injector #1 to PCM. This can be done by the color coded wires, or by a diagram of the numbered positioning of the terminal. Test continuity between the PCM plug and the injector ground terminal on the injector plug. This should ohm out if the connection is proper. If no continuity is found between the two points, it is likely that there is a split wire along the fragile wire loom that catches the firewall and splits along the valve cover loom.
Alternatively, this can be tested with the vehicle running and backplugging into the noted injector PCM terminal. Grounding to the chassis from this point will tell if the 14v is reaching the PCM uninterrupted.
If all tests have led to this point so far, bad news. It's likely an interior issue in your PCM. The circuit is functioning up until it reaches the PCM connector. That now means that the driver that pulses the injector is likely shorted or blown. In my case, it appeared the wires at the injector connector had pulled loose of their insulation, likely during a manifold gasket replacement moving around the engine bay. The direct contact without the resistance of the injector likely shorted the driver and positioned it stuck open and unable to ground. Check your harness for any damage or wear in the old brittle wiring, as something likely caused it the first time and will continue to ruin a new PCM if not corrected.
The Short Term (Redneck) Fix
On a six cylinder, inline engine there is the possibility for a short term fix. This may apply depending on your vehicle's firing order as well. For the 4.0 liter 242 engine in my rig, the crank position, and therefore timing, of cylinder #1 and #6 are simultaneous. The repair is a quick fix and I would not recommend it, take it into account at your own risk. Should it be done? Probably not. Can it? Yes, and it could get you out of some situations without running a cylinder on no fuel.
By splicing the ground of the #1 and #6 injectors, they will both be firing at the same time. I experimented with this by using a needle into the pcm ports of the #1 and #6 ground circuits, and then using a set of alligator clips to splice them. The ground is now provided by the injector #6 driver. This has potential to damage yet another injector driver as it wasn't designed.
The Long Term Repair
Have experience pulling computer boards apart and successfully getting them back together? No? This method likely isn't up your alley. There are replacement PCM units available. I would not recommend any Ebay or online vendor in the $100-200 range. Many of these have pages of reports on consumer affairs and are noted for merely flipping junkyard computers with janky repairs. Cardone does provide a unit in the $400-500 range, and although I have no experience to testify for it, appears a better option. Mopar dealers are said to offer them as well, but have been noted as also having remanufactured and no longer new units. Keep in mind that the replacement will need to follow your part #, as to provide the CA/Fed emissions and transmission type. E-vin and mileage should also be correctly refreshed into a PCM.
In the case that you're electronically inclined or have access to someone who possesses such knowledge, here's the aftermath of mine. The later model computers have a Motorola chipboard. The injector Driver on the 2000 held a part # 43U02, but pulled no results through online and distributor search. I pulled the pcm and disassembled the casing, careful not to damage the 20 year old unit. My father then handled the repair with the resources of an electrical engineer. An alternate part # was used based off comparison to the Motorola chip. This will be a Mosfet Discrete Semi-Conductor with three prongs and a surface mount. The chip specification is N-type. The install was completed with the lifting of the shorted driver, and re-solder of the new driver. A blue wire was then secured between the driver and the other portion of the chipboard; this is an old board and lifting the component may well damage the connection, the wire gave an extra assurance of continuity. Additionally, we recoated the internals with a Urethane Conformal Coating, a crucial step before final assembly.
After this repair, the Jeep started up with no CEL illuminated and no longer stored a P0201. Engine runs smooth and not with the miss the injector circuit previously caused.
Questions, Comments? Input on all things PCM and Mopar Electronics? Drop me a line below!