P1491 code

There was a thread once with that same code that ended up being caused by the alternator having gone bad. Strange but true. That there is static coming out of your radio even with your phone being plugged in kinda ties in with the alternator possibly having a problem like it might be putting out some AC (noise) on top of the pure DC it's supposed to put out.

Tds77 said:

Thanks jerry ,
Is there anything I can do to test the alternator before replacing. I tested voltage, but may be something in the alternator shorting out? To cause these issues?

Click to expand...

Take the belt off and crank it. See what happens.

Had this code randomly happen today with my 03 2.4 L. Spent a good chunk of time reading forums and sifting the FSM, and I think I have found some information that will be helpful to anyone that has this issue.

First, the specific error code P1491 is defined as a "Radiator Fan Relay Circuit Condition" based off the scanner I used with my phone. From what I have read, there are multiple reasons for this code to be thrown. The first could be a blown fuse. First check the 40A fuse in slot 4 of the power distribution center (PDC). (Ref fig 1 and fig 2).

Further looking at Figure 2, from this print it shows that these fuses are always hot, as the battery is directly connected. I confirmed this when I skipped the relay to test radiator fan functionality without the key in the ignition. In order to test to make sure the radiator fan was functioning, I used figure 3 to figure out which wires needed to be connected.

Now that I knew which wires I needed to connect to skip the relay, I had to locate where the actual radiator fan motor relay was. This is totally dependent on which year you have, in an 03 2.4L it is located on the side of the PDC, as seen in figure 4 below.

After locating the relay and disconnecting the adapter, you need to jump the blue/pink wire to the yellow wire on the adapter itself, as seen in figure 5.
Note the blue/pink wire is HOT, use the correct gauge wire to avoid melting and burning your fingertips off . For me, when I jumped these wires my fan spun, so I know it is not a radiator fan issue. If it does not spin, either the 30 Amp Circuit breaker, seen in figure 6, is blown, the fan has an issue, or you are not getting any power to the adapter itself. As far as I am aware, the only fuse that would prevent this, assuming there is no loss of any other primary function in the vehicle, is that in Figure 1 as previously discussed.

For where I am at now, I'm assuming my radiator fan motor relay is bad, which can be found here: Radiator Fan Motor Relay

As for the things I am unsure of, I do not know if there is a fuse in the glove box that can be a culprit to this. I could not find in the FSM a fuse in the fuse box that was tied to the PCD. I also tried seeing if there was a fuse tied to the PCM, specifically module C2, seen in figure 3, which I found nothing. In figure 3 it is also somewhat confusing that the module has an input from the "high speed radiator relay", but there is no specific component in the FSM or parts list called this.

I am fairly certain that the "input" from the high speed radiator relay that actuates the radiator fan motor relay is temperature driven, specifically from the engine coolant temperature sensor. From looking at the Pin-outs, as seen in figure 7, there is no mention of the relationship however, so I am stuck as to where I can go. If I had to guess, whichever data is collected from the coolant temp sensor and gathered by C1, it is used via the PCM and sent as an input to the radiator fan motor relay.

If anyone has any additional info I, as well as anyone else having this issue, would greatly appreciate it. Let me know if I gave any misleading information as well. My hopes with spending the time of making a "mini guide" were that I can eventually turn this in for submission to be added to the "how-to-guide" section of the forum. (@Jerry Bransford @Chris @Wildman this will be reformatted to be more of a how-to guide once I get some answers)

Awesome writeup!!

Strazi said:

Had this code randomly happen today with my 03 2.4 L. Spent a good chunk of time reading forums and sifting the FSM, and I think I have found some information that will be helpful to anyone that has this issue.

First, the specific error code P1491 is defined as a "Radiator Fan Relay Circuit Condition" based off the scanner I used with my phone. From what I have read, there are multiple reasons for this code to be thrown. The first could be a blown fuse. First check the 40A fuse in slot 4 of the power distribution center (PDC). (Ref fig 1 and fig 2).

View attachment 409292
Fig 1 - PDC 40 A Fuse for Radiator Relay

View attachment 409299
Fig 2 - PDC Radiator Fan Motor Relay Fuse (Proof of relation)
​

Further looking at Figure 2, from this print it shows that these fuses are always hot, as the battery is directly connected. I confirmed this when I skipped the relay to test radiator fan functionality without the key in the ignition. In order to test to make sure the radiator fan was functioning, I used figure 3 to figure out which wires needed to be connected.

View attachment 409293
Fig 3 - Radiator Fan Motor Relay Schematic
​

Now that I knew which wires I needed to connect to skip the relay, I had to locate where the actual radiator fan motor relay was. This is totally dependent on which year you have, in an 03 2.4L it is located on the side of the PDC, as seen in figure 4 below.

View attachment 409320

View attachment 409322
Fig 4 - Radiator Fan Motor Relay Location
​

After locating the relay and disconnecting the adapter, you need to jump the blue/pink wire to the yellow wire on the adapter itself, as seen in figure 5.

View attachment 409326

View attachment 409324
Fig 5 - Radiator Fan Motor Relay Location
​

Note the blue/pink wire is HOT, use the correct gauge wire to avoid melting and burning your fingertips off . For me, when I jumped these wires my fan spun, so I know it is not a radiator fan issue. If it does not spin, either the 30 Amp Circuit breaker, seen in figure 6, is blown, the fan has an issue, or you are not getting any power to the adapter itself. As far as I am aware, the only fuse that would prevent this, assuming there is no loss of any other primary function in the vehicle, is that in Figure 1 as previously discussed.

View attachment 409333

View attachment 409335
Fig 6 - Radiator Fan 30A Circuit Breaker Location
​

For where I am at now, I'm assuming my radiator fan motor relay is bad, which can be found here: Radiator Fan Motor Relay

As for the things I am unsure of, I do not know if there is a fuse in the glove box that can be a culprit to this. I could not find in the FSM a fuse in the fuse box that was tied to the PCD. I also tried seeing if there was a fuse tied to the PCM, specifically module C2, seen in figure 3, which I found nothing. In figure 3 it is also somewhat confusing that the module has an input from the "high speed radiator relay", but there is no specific component in the FSM or parts list called this.

I am fairly certain that the "input" from the high speed radiator relay that actuates the radiator fan motor relay is temperature driven, specifically from the engine coolant temperature sensor. From looking at the Pin-outs, as seen in figure 7, there is no mention of the relationship however, so I am stuck as to where I can go. If I had to guess, whichever data is collected from the coolant temp sensor and gathered by C1, it is used via the PCM and sent as an input to the radiator fan motor relay.

If anyone has any additional info I, as well as anyone else having this issue, would greatly appreciate it. Let me know if I gave any misleading information as well. My hopes with spending the time of making a "mini guide" were that I can eventually turn this in for submission to be added to the "how-to-guide" section of the forum. (@Jerry Bransford @Chris @Wildman this will be reformatted to be more of a how-to guide once I get some answers)

View attachment 409354
Fig 7 - PCM C2 Pin-out info​

Click to expand...

Update:

Looks like my guess at the relationship between the engine coolant temperature (ECT) sensor and radiator fan motor relay was correct. Reference pic below.

Update:

Tried new relay and as soon as I plugged it on the radiator came on full blast while the engine was off… lol. No matter if the engine was running or not the radiator fan was on full blast. I cleared codes to see if that was an issue, still stayed on. I disconnected the battery to reset the system, same result.

I let the engine idle until reaching ~210 degrees on the dash, so I’m assuming their is no issue with the ECT sensor.

Considering the code didn’t clear, I’m going to assume I got unlucky and the relay I received is stuck in the closed position, whereas the OEM one is stuck in the open position. Ordered a replacement.

Will update tomorrow.

Strazi said:

Update:

Tried new relay and as soon as I plugged it on the radiator came on full blast while the engine was off… lol. No matter if the engine was running or not the radiator fan was on full blast. I cleared codes to see if that was an issue, still stayed on. I disconnected the battery to reset the system, same result.

I let the engine idle until reaching ~210 degrees on the dash, so I’m assuming their is no issue with the ECT sensor.

Considering the code didn’t clear, I’m going to assume I got unlucky and the relay I received is stuck in the closed position, whereas the OEM one is stuck in the open position. Ordered a replacement.

Will update tomorrow.

Click to expand...

Update:

Tested a second new relay, and it didn't cause the fan to run when engine was off. This confirms the first new relay I got was stuck in the closed position. The next test I ran was unplugging the engine coolant temperature sensor. I repeated this test for the original OEM relay and the second new relay I got today. In both cases, the radiator fan immediately came on upon engine start.

I did another test with the ECT sensor in and revved until the temp gauge got to ~215 degrees. I noticed around this temp the gauge started to drop in temperature. I then checked the fan and what do you know, it is working! This was the case for the original OEM and new relay. I was not expecting it to work for both. This no longer looks like a relay issue, yet I still have the check engine light.

I was suspicious that my code reader wasn't picking up additional codes, so I had a local auto store test it and what do you know, a P0118 code also showed which mine did not. This error indicates a problem with the ECT sensor, which is odd considering it was reading fine on the gauge. I went ahead and replaced it, and the engine check light went away!

I won't lie what happened next was scary. Everything was running fine but coolant was leaking, so I shut the engine off and as I rounded the front fender and looked at the temp sensor it exploded out the front and sent 210 degree coolant everywhere. Luckily only a few small drops hit me but I was about 2 seconds away from getting a face full of coolant. What happened was the the temp sensor had seized itself to the brass insert, and to be honest I didn't think that much of it because I barely put any torque on it when I went to take it out. The brass insert was already partially out of the thermostat housing so the fact that it came out so easily made it seem like it was supposed to happen, and the rest is history.


I was able to replace the thermostat housing off of my dad's blown 2.4L, and it bolted right up. So far all good, hopefully no more sensor rockets!