Mechanical Repair: DIY Pop-Top Camper Build – 2000 Jeep Cherokee
Commonly found in 20+ year old jeeps and vehicles, a P0201 code or similar (P0202, P0203, P0204, P0205, P0206) indicates an issue within the electronic control of the fuel injectors.
This may be accompanied by a misfire code, and often times will majorly effect how the engine runs unless fixed right away. More on diagnostics:
The Following Post Details the DIY Diagnostic and P0201 Repair Process on a 2000 Jeep Cherokee XJ. Electrical work, especially that relating to the engine control unit, should not be attempted by those inexperienced in such fields. Work at your own risk and refer to a proper vehicle specific article as needed.
What is a P0201 Code? P0202? P0203?
A P020 code relates to a faulty electrical circuit that controls fuel injection.
In Jeep (Mopar) and similarly coded vehicles, the P020 prefix indicates a fuel injection open circuit malfunction. The last digit (P0201, P0202, P0203, etc.) identifies precisely which fuel injector circuit is problematic – with #1 being the front most cylinder counting rearward (on inline engines / Jeep 4.0).
A P0201 error will trigger the Check Engine Light and may also relate to a misfire code such as P0300, P0301, P0302, P0303, P0304, P0305, P0306, etc.
There are several steps to diagnosing this fuel injection issue, detailed below. Above all – this is an electrical issue and is typically not caused by physical fuel flow to the likes of fuel pumps, fuel lines, fuel filters, etc.
What Causes a P0201 Code?
A P0201, P0202, P0203, P0204, P0205, or P0206 code may appear after replacing Fuel Injectors, Lines, or even unrelated parts such as an Intake Manifold, Exhaust Manifold, Gasket, etc. Why is this?
Many electrical parts make up modern fuel injection systems. When working on or around the engine wire harness, brittle factory wires may break or short and cause P0201 or related electrical issues.
It is also possible for old fuel injectors to have faulty electrical components. Newly replaced injectors may have poor quality control from the factory.
A shorted or faulty ECU (Engine Control Unit) can also bring complications and added cost to the repair. This is detailed further below, but should be considered after a simple set of diagnostics:
P0201 Jeep Cherokee Specific Diagnosis
The following diagnosis process is typical for a 2000 Jeep Cherokee, but may relate to other vehicles, particularly Mopar (Chrysler, Dodge, Ram).
It is always best to refer to a vehicle specific electrical diagram to identify the proper components and diagnostic steps.
Can a Bad Fuel Injector Cause P0201?
It’s possible that a bad fuel injector is the cause of a P0201, P0202, P0203, P0204, P0205, or P0206 check engine light. This can be the result of either a high mileage injector or a newer injector with faulty components.
There is a simple test to rule out a faulty fuel injector. A P0201 code is specific to Injector #1. P0202 is specific to Injector #2, and so on. If the injector is faulty, swapping the position of two injectors would cause a different P020 code to appear.
This is because the P0201 code is specific to cylinder location. If the code is unchanged after swapping fuel injector locations, it is not due to a faulty injector.
ASD Relay & P0201 Fuel Injector Circuit Open
The first step in locating a fuel injector circuit fault is to trace the path of power. The circuit should be tested on both sides of the injectors (+12v and ground) to find all related malfunctions.
This is where the ASD Relay comes into play:
What is an ASD Relay?
An ASD, or Auto Shutdown Relay, provides 12v power to components such as the fuel injectors. This relay is triggered by the ignition switch. The auto shutdown function ensures that the fuel system is only operating while the vehicle is running.
In the case of the 2000 Cherokee, the ASD (Auto Shutdown Relay) provides 12v (+) to all six fuel injectors. A faulty Auto Shutdown Relay could prevent power from reaching the fuel injectors at all.
Where is a Jeep Auto Shutdown Relay Located?
The location of the auto shutdown relay on a Jeep Cherokee (XJ) is inside of the main relay/fusebox of the engine bay. The ASD relay is pictured in the upper left corner, just above the cooling fan relay.
How To Check ASD Relay – Jeep Fuel Injection:
Although a faulty ASD relay would seemingly cause none of the fuel injectors to work, it is quick work to ensure that the Jeep fuel injectors are receiving a full 12v (+) at all connections.
The 12v (+) output from the Jeep ASD relay is typically a factory Dark-Green/Orange wire. This wire splices to all six injectors’ positive terminals.
Using a standard DC capable multimeter, check that there is 12v (+) at each injector electrical connector coming from the positive 12v (+) wire.
Diagnostic Results: In the case of the 2000 Jeep Cherokee Build, ~14v was present at all six fuel injector positive terminals. The test was performed while the jeep was running.
The issue was not related to the Auto Shutdown Relay.
What if One Fuel Injector Does Not Have 12v Power?
The Auto Shutdown Relay provides power to all fuel injectors through a single spliced circuit (2000 Jeep Cherokee). A failed relay would likely not cause a single fuel injector to lose power. In this case, it is likely that the positive wire from the ASD relay to the injector has broken or shorted.
A replacement wire should be properly routed and soldered in place in the case of no power at a single fuel injector connector.
P0201 Fuel Injection Circuit Ground (-)
If the ASD relay and 12v (+) test above uncovers no issues, there is likely an issue with the ground (-) side of the circuit.
Again, sourcing a vehicle-specific repair manual with a detailed electric diagram will help pinpoint exactly which components to check.
How a Fuel Injection Ground Circuit Works:
In the case of a 97-01 Jeep Cherokee, the fuel injector is controlled through a pulsated ground signal (-).
A driver inside of the ECU (Engine Control Unit) rapidly opens and closes the circuit by momentarily providing ground to the injector. This signal is tuned to factory specifications and relies upon readings from the CPS (crankshaft position sensor) among other sensors to dial in fuel injection timing.
The ECU uses this electrical control to deliver fuel in the right amount, at just the right time. The ECU relies upon a common ground (-) to do so.
*PCM (Powertrain Control Module) is often used interchangeably with the term ECU (Engine Control Unit)
Can a Bad Ground Cause P0201?
A bad ground can cause an open fuel injector circuit, resulting in a P0201, P0202, P0203, P0204, P0205, or P0206 code. But this isn’t a typical ground:
If the common ground (-) to the ECU/PCM was faulty, there would likely be greater issues with engine control, including ignition/starting/running.
The pulsated fuel injector ground provided by the ECU is controlled internally and only switched on for a fraction of a second at a time. It is not possible to check the ground connection through resistance (ohming out).
Fuel Injector Ground – How To Diagnose:
A fuel injector circuit should be diagnosed using a noid light kit. This kit uses a simple ~12v capable bulb with electrical prongs specific to the manufacturer’s wiring harness.
Performed while the vehicle is running, the noid light reveals the following:
1. Rapidly Blinking Noid Light
A rapid and regularly blinking noid light indicates proper fuel injector circuit function. The light illuminates each time the ECU pulses ground.
2. Solid Noid Light
A solid noid light indicates a fuel injector circuit that is stuck closed (on). If the fuel injector were to remain hooked up, fuel would be dumped into the cylinder constantly. This would cause misfire, cylinder fuel washing, and gasoline coming out of the exhaust. This could turn catastrophic quickly.
3. Noid Light Doesn’t Light Up
A noid light that shows no illumination indicates that the injector circuit is either not receiving constant 12v power (+), or no pulsated ground signal (-).
The noid light should be checked against other cylinders’ fuel injectors to ensure proper use/connection. If the light is in fact hooked up properly:
– Check constant 12v (+) at the fuel injector terminal as detailed above
– Diagnose why the fuel injector terminal is not seeing any ground (-)
Identifying Bad Fuel Injector Ground:
Thin and heat-brittled factory wiring can cause a break in the ground circuit. This can be traced between the fuel injector and the ECU/PCM.
There are few options to find a bad injector ground besides splitting open the wire casing and tracing it back to the Jeep/Vehicle’s computer:
Important: When Splitting/Working on Any Wires, Unplug the Vehicle’s Battery. Ensure All Wiring is Properly Insulated and Routed Before Providing Power. Electrical Work Should Not Be Taken Lightly.
P0201 Multimeter Ground Test
A multimeter should be used to check for a broken ground wire. Test continuity between the ECU harness connector and the fuel injector electrical connector. If the two connectors do not “ohm out”, showing 0.00 ohms resistance, there is likely a break somewhere in the wiring harness.
A detailed repair manual w/ wiring diagram shows which color wires to test
Further Isolating a Bad Ground (-)
1. Faulty Fuel Injector Electrical Connector
It is possible that the positive or ground wire has simply separated from the injector’s hardwired electrical connector. Often times pushing the wire slightly into the connector during the noid test can reveal a spotty connection. Solder in a new connector as necessary.
2. Bad/Broken Fuel Injector Wiring Harness
The factory wiring in any old jeep has seen years of heat baking engine temperatures and oil/fuel exposure. Factory insulation can easily be broken or chafed. Oftentimes this wiring remain intact until moved/worked on.
This problem presented itself on the 2000 Cherokee after a complete engine replacement – even with precautions taken to keep wiring intact.
Soldering factory wire back together and reinsulating is a quick repair.
Want added insurance? Keep reading below. A short in any of the wiring can cause irreparable damage to internal ECU components.
3. Internal ECU Damage
An untraceable P0201 code may be the result of internal ECU/PCM damage. Wiring issues (mentioned above) can cause a short between a positive 12v (+) wire and the fuel injector ground wire (-). This was the case with the 2000 Jeep Cherokee. Further detailed and solved below:
P0201 Jeep Defective Wiring
An electrical short from old or brittle Jeep wiring can cause internal damage to the vehicle’s control system (ECU/PCM). Resulting in a P0201 code, here’s why the factory wiring can cause irreparable damage:
No Fuse or Failsafe – Fuel Injection Circuit
There is no internal fuse to the Jeep Cherokee ECU/PCM to protect from a shorted fuel injector. As such, any short in the 12v (+) and Ground (-) wires can cause irreparable damage to the internal computer board.
Fuel Injector Resistance
The 97-01 Jeep Cherokee has a fuel injector resistance of 10.8 to 13.8 ohms.
When a shorted wire or faulty injector causes 12v to reach the ECU with no resistance, it is likely that the internal driver chip will be overpowered.
12v (+) and Ground (-) Wires Spliced Together
On many models of Jeeps (particularly the 87-01 Cherokee), the factory packaged both 12v (+) and ground (-) fuel injector wires side by side.
Yes, each wire has its own respective electrical insulation and identifying color. But on a 20+ year old Jeep it only takes a small split in brittle insulation to short out ECU internals.
DIY Redesign: Fixing Jeep Defective Wiring
**Electrical work should be performed only by those with proper experience/knowledge.
A “redesigned” way to insure against these shorts is to run entirely new insulated automotive wire (22AWG+) with the following installation method:
- Package ground (-) wires together in one harness, wrapped with 3M Super 33+ electrical tape (the good stuff). Route the ground (-) harness from the ECU to the fuel injector rail.
- Package 12V (+) wires together in one harness, also properly wrapped and insulated from each other.
- The final ~10″ of each set of injector wires (12v and ground) will need to be run side by side to the injector electrical connector. For added insurance, each wire may be further wrapped in insulating electrical tape, braided sleeving and/or heat shrink.
- Solder in new OEM fuel injector electrical connectors. After all this work, there is no point in leaving an old brittle fuel injector harness connector. These can be purchased online or through many auto parts stores.
- Adding Fuses: As a last overkill modification, the 2000 Cherokee had a fuse block wired individual to each ground circuit. Located close to the ECU, the fuse block holds 1-amp mini fuses.
*It is uncertain what level of protection fuses provide to such a low-amperage pulsated circuit. The concept here is to protect from a constant short. Overkill? Yes. But untamed electrical shorts can wreak havoc.
P0201 Jeep ECU Repair
If an electrical short has occurred within the fuel injector circuit, it is likely that the Jeep ECU/PCM has been internally damaged and needs replaced.
Electrician Repair
**The following excerpt is provided for entertainment/documentation and is not intended as a how-to. Electrical work should be done at your own risk only under the responsibility of a professional automotive electrician.
An internal chip controls the Fuel Injector Circuit’s ground.
This driver provides a pulsated ground (-) under the tune of the ECU/PCM.
Under further diagnosis of the 2000 Jeep Cherokee Build’s P0201 code, a blown driver was found and researched further before being repaired.
Jeep ECU/PCM Fuel Injector Driver
The observed part number in the OEM 2000 Jeep Cherokee computer:
Motorola P/N 43U02
A similarly spec’d Mosfet Discrete Semiconductor was sourced with the help of a senior electrical engineer. The damaged driver was then lifted and the replacement soldered in place with further precautions added.
Unfortunately, the 2000 Cherokee only had the problem areas of the OEM wiring harness mended before installing the repaired ECU. Months later another short in the OEM harness caused irreparable circuit board damage.
Likely the prognosis for many at this point, a refurbished ECU was sourced and fixed the problem with less hands on expertise. Detailed Below:
P0201 Jeep ECU Replacement
An internally damaged Jeep ECU is likely irreparable by most mechanics. There are a few options for replacement on a Jeep Cherokee or similar out-of-production vehicle:
- OEM Jeep Dealer ECU
It has been said that select Jeep dealers (Mopar – Chrysler, Dodge, Jeep Ram) can order a proper OEM ECU for a Jeep Cherokee or similar vehicle. As time goes on these replacement units may grow obsolete.
It is said that these units are Mopar refurbished (Jeep Forum Intel). It may also be possible to get the required factory flash with this method to report correct mileage and e-vin for Smog. - Non-Dealer All-In-One Replacements
There are few companies found through google that offer supposed replacement units with re-flashing available.
These Vendors are NOT recommended. Here’s Why:
Many of the vendors have a so-so online presence. Better Business reviews often allege that they send bricks: janky salvaged junkyard computers. These are reportedly not re-flashed as promised. A sketchy industry to say the least – be alert before purchasing online. - DIY ECU Sourcing
Sourcing a proper ECU can be tricky, as for Jeep Cherokees the ECU changed several times through the model years. A general rule of thumb is that the hardware should be sourced specific to model year.
The transmission and emissions type (CA vs. FED) may be overlooked if re-flashing. You may have luck finding a pick-and-pull junkyard ECU, but in the case of the 2000 Cherokee Build, a Mopar refurbished unit was sourced on Ebay from a reputable reseller of used OEM parts.
Why Does a Jeep ECU Need Reflashed?
Jeep ECU’s and many other modern OBDII+ vehicle control systems have specifically programed tuning specifications. The ECU software (re-flash) needs to match both the transmission type and emissions type to eliminate trouble codes and allow for proper engine and transmission operation.
Further, e-vin and accurate milage are programmed into the Jeep Cherokee ECU, not the odometer, and must be accurate for registration/smog or inspection in most states.
How to Re-flash Jeep ECU:
OBDII Jeep computers, as found in the 2000 Jeep Cherokee, are not easily tunable by most mechanics, unlike other vehicle manufacturers.
The JTEC ECU system is encrypted and only editable through costly licensing and a factory-specific device. You may find a dealer that is willing to do the factory reflash. Outside of this, there are only a few tuners online that have a reputable track record of working with JTEC computers.
A quick search on Jeep Forums (especially stroker build forums) is a solid lead to follow if pursuing the DIY route. Some tuners re-flash via mail.
Fuel Injection Circuit Repair Steps:
To recap the full depth of information above into manageable steps:
- Source a Repair Manual w/ Full Electrical Diagrams
- Noid Light Test For Fuel Injection Circuit Diagnosis
- Test 12v (+) power from Auto Shutdown Relay
- Test Continuity Between ECU Connector and Injector Connector
- Identify & Repair Exposed Injector Circuit Wiring
- Source & Install a Replacement ECU (If Required)*
*ECU should only be replaced after all wiring issues are repaired – or it will fry itself again.
P0201 Jeep Repair Outcome:
After researching, carrying out, and backtracking through the above steps, the 2000 Jeep Cherokee Build proved roadworthy again. Since rewiring the fuel injectors in full and replacing the damaged ECU the Jeep has presented no check engine lights. California Smog passed just fine.
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Keep on keepin’ on!
DIY Pop-Top – Finished Redesign (Fiberglass Mold & Production)
