Some car owners keep older vehicles longer than they should, and maybe it's due to a love affair with a brand or model. With jeeps this is often the case, similar to older BMW or Mercedez-Benz models. The positive side is you've probably worked on these models for a long and know them well. Common problems, repair procedures and what to expect when tearing into one. However, every common problem won't always have the same fix. This blog post talks about how we helped a shop repair a 2000 Jeep Wrangler with an ASD Relay that was not activating, causing a no start condition.
The shop called us for help late in the repair process, they already installed a new ASD relay and was about to install a new powertrain control module (PCM).
With the key in RUN position, the ASD relay would buzz and there was no MIL light. The missing MIL light indicated a fault with the PCM as did the buzzing relay.
What I love at as a support technician at AutologicLive, is the mechanic on the other end can send me live images of what they are currently testing, like below. They want to be sure they were using the right wiring diagram, so I compared what they were using with my info. They were also able to send all the photos used in this article directly through their MVDS tablet.
Checking the relay confirmed power at terminals A13 and A15. Both power feeds were able to hold a load at the power distribution box.
Power to PCM from ASD relay on PCM connector C3 Pin 12 (dg/pk wire) was not present.
Relay control circuit at PCM connector C3 Pin 3 (db/yl wire) was fluctuating between 8 and 4 volts. The PCM was trying to hold the relay coil to ground but could not. If I added a ground, the relay would activate and stop buzzing. The problem was at the PCM as suspected.
Next up was to test PCM power and grounds.
Both Grounds (PCM connector C1 Pins A32, A31 (bk/tn wires)) were good with a value of 0.01 volts, and a value of 0.02 when loaded. These were checked backprobing connector and connector unplugged.
Power at PCM connector C1 Pin A2 (db wire) was good with a value of battery volts and held when loaded. This was tested backprobing and connector unplugged. Notice when loading the circuit I have the tech use an incandescent bulb style test light. These test lights can add a good load to the circuit safely. I am planning on sharing my thoughts on this topic in an upcoming blog post.
Power at PCM connector C1 Pin A22 (rd/wt) was good when backprobed with a value of battery volts and held when loaded. When I had the tech unplug the PCM connector and tested again only 8.13 volts were present. When I loaded the circuit voltage disappeared. Since voltage was good on the backside of the connector I knew it would be in the connector itself.
The tech disassembled the connector and the problem was found. A corroded pin on the PCM connector. After replacing the pin the vehicle functioned normally. The vehicle was fixed, the customer was happy and another classic stays running - until the next issue.
Like I mentioned earlier. The common problems aren't always so common. Due to the age of this vehicle, a corroded terminal caused what some may assume is a quick part swap. Need help with a similar problem? Send me a request through your Autologic AssistMobile App.